Techniques for beam shaping at a millimeter wave base station and a wireless device and fast antenna subarray selection at a wireless device

ABSTRACT

Methods, systems, and devices are described for wireless communication at a user equipment (UE). A wireless communications system may improve UE discovery latency by dynamically selecting and switching beam forming codebooks at the millimeter wave base station and the wireless device. Selecting an optimal beam forming codebook may allow the wireless communication system to improve link margins between the base station without compromising resources. In some examples, a wireless device may determine whether the received signals from the millimeter wave base station satisfy established signal to noise (SNR) thresholds, and select an optimal beam codebook to establish communication. Additionally or alternately, the wireless device may further signal the selected beam codebook to the millimeter wave base station and direct the millimeter wave base station to adjust its codebook based on the selection.

CROSS REFERENCES

The present application for patent claims priority to U.S. ProvisionalPatent Application No. 62/100,350 by Raghavan et al., entitled“Techniques for Beam Shaping at a Millimeter Wave Base Station and aWireless Device,” filed Jan. 6, 2015, and U.S. Provisional PatentApplication No. 62/100,352 by Raghavan et al., entitled “Techniques forFast Selection of an Antenna Subarray and Beamforming for MillimeterWave Wireless Connections,” filed Jan. 6, 2015, both assigned to theassignee hereof, and expressly incorporated by reference herein.

BACKGROUND

Field of Disclosure

The following relates generally to wireless communications, and morespecifically to techniques for beam shaping at a millimeter wave basestation and for fast selection of an antenna subarray at a wirelessdevice.

Description of Related Art

Wireless communications systems are widely deployed to provide varioustypes of communication content such as voice, video, packet data,messaging, broadcast, and so on. These systems may be multiple-accesssystems capable of supporting communication with multiple users bysharing the available system resources (e.g., time, frequency, andpower). Examples of such multiple-access systems include code divisionmultiple access (CDMA) systems, time division multiple access (TDMA)systems, frequency division multiplexing access (FDMA) systems, andorthogonal frequency division multiple access (OFDMA) systems, (e.g., aLong Term Evolution (LTE) system).

By way of example, a wireless multiple-access communications system mayinclude a number of base stations, each simultaneously supportingcommunication for multiple communications devices, which may beotherwise known as user equipment (UEs). A base station may communicatewith the communications devices on downlink channels (e.g., fortransmissions from a base station to a UE) and uplink channels (e.g.,for transmissions from a UE to a base station).

Various communication systems may use different frequency bandsdepending on the particular needs of the system. For example, amillimeter wave frequency band (which may be between 30 to 300 GHz) maybe used where a large concentration of UEs are relatively close to oneanother and/or where a relatively large amount of data is to betransferred from a base station to one or more UEs, or vice versa.Millimeter wavelength signals, however, frequently experience high pathloss, and as a result, directional beam forming techniques may be usedfor uplink (UL) and/or downlink (DL) transmissions between a basestation and a UE using millimeter wavelength frequencies. Directionalbeamforming techniques may enable a transmitter to transmit a signalonto a particular propagation path, and may enable a receiver to receivea signal from a particular propagation path. In this case more than onesignal propagation path may exist between a UE and a base station. Thereliance on directional beams, however, may make millimeter wavecommunications more resource-intensive.

The base station and the UE may each use multiple antennas whencommunicating with each other. Multiple antennas at the base station andUE may be used to take advantage of antenna diversity schemes that mayimprove communication rate and/or its reliability. There are differenttypes of techniques that may be used to implement an antenna diversityscheme. For example, transmit diversity may be applied to increase thesignal to noise ratio (SNR) at the receiver for a single data stream.Spatial diversity may be applied to increase the data rate bytransmitting multiple independent streams using multiple antennas.Receive diversity may be used to combine signals received at multiplereceive antennas to improve received signal quality and increasedresistance to fading. However, in some cases, a position of the handholding the mobile device and/or near-field effects due to the body mayinterfere with signals received at a plurality of antennas at the UE.

SUMMARY

Systems, methods, and apparatuses for beam shaping at a millimeter wavebase station, and for fast selection of an antenna subarray at awireless device are described. In accordance with the presentdisclosure, a wireless communications system may improve user equipment(UE) discovery latency by dynamically selecting and switchingbeamforming codebooks at the millimeter wave base station and thewireless device. Selecting an optimal beamforming codebook may allow thewireless communication system to improve link margins between the basestation without compromising resources. In some examples, a wirelessdevice may determine whether the received signals from the millimeterwave base station satisfy established signal to noise (SNR) thresholds.The wireless device may then select an optimal beam codebook toestablish communications with the millimeter wave base station.Additionally or alternately, the wireless device may further signal theselected beam codebook to the millimeter wave base station and directthe millimeter wave base station to adjust its codebook based on theselection.

In accordance with the present disclosure, the user equipment (UE) mayscan through a plurality of antenna subarrays one at a time with asingle beamforming vector to estimate the signal to noise ratio (SNR) atthe plurality of antenna subarrays. Based on the estimated SNR, the UEmay determine whether the received signals are above or below anestablished SNR threshold level at the plurality of antenna subarrays.In some examples, the UE may select an antenna subarray from a pluralityof scanned antenna subarrays that offers the desired signal quality.Additionally or alternately, the UE, after selecting an antennasubarray, may further refine the codebook of beamforming vectors at theUE and the base station in order to achieve improved link margins forthe subsequent data phase between the base station and the UE.

In one example, a method of communications at a wireless device isdescribed. The method may include receiving, at a wireless device, afirst signal from a millimeter wave base station using a first beamcodebook, dynamically determining that a second beam codebook, differentfrom the first beam codebook, is to be used on the transmitted firstsignal, and transmitting a second signal to the millimeter wave basestation requesting the millimeter wave base station to use the secondbeam codebook.

In one example, an apparatus for communications at a wireless device isdescribed. The apparatus may include means for receiving, at a wirelessdevice, a first signal from a millimeter wave base station using a firstbeam codebook, means for dynamically determining that a second beamcodebook, different from the first beam codebook, is to be used on thetransmitted first signal, and means for transmitting a second signal tothe millimeter wave base station requesting the millimeter wave basestation to use the second beam codebook.

In one example, a further apparatus for communications at a wirelessdevice is described. The apparatus may include a processor, memory inelectronic communication with the processor, and instructions stored inthe memory, wherein the instructions are executable by the processor toreceive, at a wireless device, a first signal from a millimeter wavebase station using a first beam codebook, dynamically determine that asecond beam codebook, different from the first beam codebook, is to beused on the transmitted first signal, and transmit a second signal tothe millimeter wave base station requesting the millimeter wave basestation to use the second beam codebook.

In one example, a non-transitory computer-readable medium storing codefor communication at a wireless device is described. The code mayinclude instructions executable to receive, at a wireless device, afirst signal from a millimeter wave base station using a first beamcodebook, dynamically determine that a second beam codebook, differentfrom the first beam codebook, is to be used on the transmitted firstsignal, and transmit a second signal to the millimeter wave base stationrequesting the millimeter wave base station to use the second beamcodebook.

Some examples of the method, apparatuses, or non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for determining whether a quality ofthe received first signal is above or below a first threshold,dynamically selecting the second beam codebook based at least in part onthe determining, and transmitting the second signal to the millimeterwave base station identifying the selected second beam codebook.Additionally or alternately, some examples may include processes,features, means, or instructions for determining whether the quality ofthe first signal is above or below a second threshold, and dynamicallyselecting the second beam codebook based at least in part on thedetermining. Additionally or alternately, in some examples the secondsignal includes a signal energy estimate, a beamforming vector index,information for beamforming, or a combination thereof.

Some examples of the method, apparatuses, or non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for identifying a first receiver beamcodebook used at the wireless device as being associated with the firstbeam codebook used by the millimeter wave base station, and requesting aswitch from the first receiver beam codebook to a second receiver beamcodebook associated with the second beam codebook used by the millimeterwave base station. In some examples, the request can be based at leastin part on hardware and/or software complexity issues for the radiofrequency chains (e.g., phase shifters, analog-to-digital converters,up/down converters and/or mixers, digital-to-analog converters, radiofrequency circuitry needed to establish the links, and the like),maintenance of link issues, and/or performance improvement with metricssuch as rate, reliability, or a combination thereof. Additionally oralternately, some examples may include processes, features, means, orinstructions for adapting the first threshold based at least in part onthe selection of the second beam codebook.

In some examples of the method, apparatuses, or non-transitorycomputer-readable medium described above, the second beam codebook isselected in response to determining that the quality of signal fallsbelow the first threshold. Additionally or alternately, in some examplesthe first beam codebook is a coarse codebook and the second beamcodebook is selected from a group comprising a pseudo-omni beam patterncodebook, an antenna selection codebook, a coarse codebook of broadbeams, an intermediate codebook of slightly narrower beams, a finecodebook of narrowest beams, a wireless-device specific codebook basedon prior information at the millimeter wave base station about thewireless device, a beam negation codebook such as a codebook of beamsoptimally designed to minimize interference due to simultaneouscoordinated transmissions to multiple wireless devices, a codebook ofbeams trading off signal quality to a specific wireless device at thecost of interference to other wireless devices, or a combination ofbeamforming vectors from different codebooks.

In some examples of the method, apparatuses, or non-transitorycomputer-readable medium described above, the second signal comprises arequest for the millimeter wave base station to switch to a second beamcodebook, where the request may be based at least in part on hardwareand/or software complexity issues for the radio frequency chains (e.g.phase shifters, analog-to-digital converters, up/down converters and/ormixers, digital-to-analog converters, radio frequency circuitry neededto establish the links, and the like.), maintenance of link issues,and/or performance improvement with metrics such as rate, reliability,or a combination thereof. Additionally or alternately, some examples mayinclude processes, features, means, or instructions for transmitting thesecond signal via a random access channel (RACH) using a coarsecodebook.

Some examples of the method, apparatuses, or non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for transmitting the second signal overa low-frequency carrier network coexisting with a millimeter wavecarrier network. Additionally or alternately, in some examples thesecond signal comprises a distress signal transmitted with a uniqueidentification at a high code rate. A high code rate signal is one wherethe redundancy for overcoming noise and fading uncertainties is highwith the useful information at a much lower rate, which ensures reliableinformation recovery in poor channel conditions.

In some examples of the method, apparatuses, or non-transitorycomputer-readable medium described above, the first signal is adirectional primary synchronization signal (DPSS). Additionally oralternately, some examples may include processes, features, means, orinstructions for calculating a signal-to-noise ratio (SNR) of the firstsignal to determine a quality of the first signal.

In one example, another method of communications at a wireless device isdescribed. The method may include receiving, at a wireless device, afirst signal from a millimeter wave base station, the first signalbeamformed on a plurality of beamforming vectors from a first codebook,scanning at least a portion of a plurality of antenna subarrays with aplurality of beamforming vectors from a subarray selection codebook toidentify the quality of the first signal received at the portion of theplurality of antenna subarrays, and selecting an antenna subarray fromthe scanned portion of the plurality of antenna subarrays based at leastin part on the identified quality of the first signal.

In one example, another apparatus for communications at a wirelessdevice is described. The apparatus may include means for receiving, at awireless device, a first signal from a millimeter wave base station,means for scanning at least a portion of a plurality of antennasubarrays with a plurality of beamforming vectors from a subarrayselection codebook to identify the quality of the first signal receivedat the portion of the plurality of antenna subarrays, and means forselecting an antenna subarray from the scanned portion of the pluralityof antenna subarrays based at least in part on the identified quality ofthe first signal.

In one example, a further apparatus for communications at a wirelessdevice is described. The apparatus may include a processor, memory inelectronic communications with the processor, and instructions stored inthe memory, wherein the instructions are executable by the processor toreceive, at a wireless device, a first signal from a millimeter wavebase station, scan at least a portion of a plurality of antennasubarrays with a plurality of beamforming vectors from a subarrayselection codebook to identify the quality of the first signal receivedat the portion of the plurality of antenna subarrays, and select anantenna subarray from the scanned portion of the plurality of antennasubarrays based at least in part on the identified quality of the firstsignal.

In one example, another non-transitory computer-readable medium storingcode for communications at a wireless device is described. The code mayinclude instructions executable to receive, at a wireless device, afirst signal from a millimeter wave base station, scan at least aportion of a plurality of antenna subarrays with a plurality ofbeamforming vectors from a subarray selection codebook to identify thequality of the first signal received at the portion of the plurality ofantenna subarrays, and select an antenna subarray from the scannedportion of the plurality of antenna subarrays based at least in part onthe identified quality of the first signal.

In some examples of the method, apparatuses, or non-transitorycomputer-readable medium described above, the subarray selectioncodebook may include a coarse codebook of broad beams covering a widebeamspace area optimally designed to minimize the wireless devicediscovery latency at the cost of peak beamforming gain. The subarrayselection codebook may also include an intermediate codebook of slightlynarrower beams covering a smaller beamspace area and corresponding toanother point in the tradeoff curve between wireless device discoverylatency and peak beamforming gain. The subarray selection codebook mayalso include a fine codebook of the narrowest beams covering thesmallest beamspace area and corresponding to the highest peakbeamforming gain. The subarray selection codebook may also include acodebook appropriately designed to mitigate near-field impairments atthe wireless device. The subarray selection codebook may also include acodebook with a special structure appropriately designed to assist inchannel estimation tasks at the wireless device. The subarray selectioncodebook may also include a codebook with a special structureappropriately designed to assist in radio-frequency hardware and/orsoftware complexity reduction, reduce system complexity or cost. Thesubarray selection codebook may also include a pseudo-omni beam patterncodebook, or an antenna selection codebook. The subarray selectioncodebook may also include any combination of beamforming vectors fromdifferent codebooks thereof.

Some examples of the method, apparatuses, or non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for determining whether the quality ofthe first signal at the selected antenna subarray is above or below afirst threshold, and transmitting a second signal to the millimeter wavebase station based at least in part on the determining. Additionally oralternately, some examples may include processes, features, means, orinstructions for scanning a plurality of beamforming vectors from acoarse codebook upon determining that the quality of the first signal atthe selected antenna subarray is below the first threshold, andidentifying a first beamforming vector from the plurality of beamformingvectors based at least in part on the scanning.

Some examples of the method, apparatuses, or non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for receiving, at the wireless device,a third signal from a millimeter wave base station, the third signalbeamformed on a plurality of beamforming vectors from a second codebook,scanning a plurality of beamforming vectors from the second codebook,identifying a second beamforming vector from the plurality ofbeamforming vectors from the second codebook based at least in part onthe scanning.

Some examples of the method, apparatuses, or non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for determining that the quality of thefirst signal at the selected antenna subarray is below a secondthreshold, and identifying a beamforming vector from the plurality ofbeamforming vectors based at least in part on the determining, whereinthe beamforming vector is identified from a subarray selection codebook.

A subarray selection codebook can include a coarse codebook of broadbeams covering a wide beamspace area optimally designed to minimize thewireless device discovery latency at the cost of peak beamforming gain.Additionally or alternately, the subarray selection codebook can includean intermediate codebook of slightly narrower beams covering a smallerbeamspace area and corresponding to another point in the tradeoff curvebetween wireless device discovery latency and peak beamforming gain.Additionally or alternately, the subarray selection codebook can includea fine codebook of the narrowest beams covering the smallest beamspacearea and corresponding to the highest peak beamforming gain.Additionally or alternately, the subarray selection codebook can includea codebook appropriately designed to mitigate near-field impairments atthe wireless device. Additionally or alternately, the subarray selectioncodebook can include a codebook with a special structure appropriatelydesigned to assist in channel estimation tasks at the wireless device.Additionally or alternately, the subarray selection codebook can includea codebook with a special structure appropriately designed to assist inradio-frequency design, reduce system complexity or cost. Additionallyor alternately, the subarray selection codebook can include apseudo-omni beam pattern codebook, and/or an antenna selection codebook.Additionally or alternately, the subarray selection codebook can includea combination of beamforming vectors from different codebooks.

Additionally or alternately, some examples may include processes,features, means, or instructions for initiating an on-demand search toidentify a second beamforming vector from a plurality of beamformingvectors at the millimeter wave base station, wherein the secondbeamforming vector is identified from a group comprising at least one ofa pseudo-omni beam pattern codebook, an antenna selection codebook, acoarse codebook, an intermediate codebook, a fine codebook, a near-fieldimpairment mitigation codebook, a channel estimation codebook, acomplexity reduction codebook, or a wireless device specific codebook.

Some examples of the method, apparatuses, or non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for adapting the first threshold basedat least in part on a selection of a beamforming vector by the wirelessdevice. Additionally or alternately, some examples may includeprocesses, features, means, or instructions for transmitting the secondsignal via a random access channel (RACH).

Some examples of the method, apparatuses, or non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for transmitting the second signal overa low-frequency carrier network coexisting with a millimeter wavecarries network. Additionally or alternately, in some examples thesecond signal may be transmitted via a highly-coded low-ratechannel/network already established with a unique identification.Additionally or alternately, in some examples the second signalcomprises a signal energy estimate, a beamforming vector index,information for beamforming, or a combination thereof.

Some examples of the method, apparatuses, or non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for calculating a signal-to-noise ratioof the first signal to determine the quality of the first signal.Additionally or alternately, in some examples the first signal is adirectional primary synchronization signal (DPSS).

The foregoing has outlined rather broadly the features and technicaladvantages of examples according to the disclosure in order that thedetailed description that follows may be better understood. Additionalfeatures and advantages will be described hereinafter. The conceptionand specific examples disclosed may be readily utilized as a basis formodifying or designing other structures for carrying out the samepurposes of the present disclosure. Such equivalent constructions do notdepart from the scope of the appended claims. Characteristics of theconcepts disclosed herein, both their organization and method ofoperation, together with associated advantages will be better understoodfrom the following description when considered in connection with theaccompanying figures. Each of the figures is provided for the purpose ofillustration and description only, and not as a definition of the limitsof the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

A further understanding of the nature and advantages of the presentdisclosure may be realized by reference to the following drawings. Inthe appended figures, similar components or features may have the samereference label. Further, various components of the same type may bedistinguished by following the reference label by a dash and a secondlabel that distinguishes among the similar components. If just the firstreference label is used in the specification, the description isapplicable to any one of the similar components having the same firstreference label irrespective of the second reference label.

FIG. 1 illustrates an example of a wireless communications system inaccordance with various aspects of the present disclosure;

FIG. 2 illustrates an example of a wireless communications subsystem inaccordance with various aspects of the present disclosure;

FIG. 3 illustrates an example of a wireless communications subsystem inaccordance with various aspects of the present disclosure;

FIGS. 4A and 4B illustrate an example of a block diagram for beamshaping at a millimeter wireless device in accordance with variousaspects of the present disclosure;

FIG. 5 shows a block diagram of a user equipment (UE) configured forbeam shaping at a millimeter wave base station and/or fast selection ofan antenna subarray at a wireless device in accordance with variousaspects of the present disclosure;

FIG. 6 shows a block diagram of a UE configured for beam shaping at amillimeter wave base station and a wireless device in accordance withvarious aspects of the present disclosure;

FIG. 7 shows a block diagram of a communications management moduleconfigured for beam shaping at a millimeter wave base station and awireless device in accordance with various aspects of the presentdisclosure;

FIG. 8 shows a block diagram of a UE configured for fast selection of anantenna subarray and beamforming for millimeter wave wirelessconnections in accordance with various aspects of the presentdisclosure;

FIG. 9 shows a block diagram of a communication management moduleconfigured for fast selection of an antenna subarray and beamforming formillimeter wave wireless connections in accordance with various aspectsof the present disclosure;

FIG. 10 illustrates a block diagram of a system including a UEconfigured for beam shaping at a millimeter wave base station and/orfast selection of an antenna subarray at a wireless device in accordancewith various aspects of the present disclosure;

FIG. 11 shows a flowchart illustrating a method for beam shaping at amillimeter wave base station and a wireless device in accordance withvarious aspects of the present disclosure;

FIG. 12 shows a flowchart illustrating a method for beam shaping at amillimeter wave base station and a wireless device in accordance withvarious aspects of the present disclosure;

FIG. 13 shows a flowchart illustrating a method for beam shaping at amillimeter wave base station and a wireless device in accordance withvarious aspects of the present disclosure;

FIG. 14 shows a flowchart illustrating a method for beam shaping at amillimeter wave base station and a wireless device in accordance withvarious aspects of the present disclosure;

FIG. 15 illustrates an example of a process flow for beam shaping at amillimeter wave base station and a wireless device in accordance withvarious aspects of the present disclosure;

FIG. 16 shows a flowchart illustrating a method for fast selection of anantenna subarray and beamforming for millimeter wave wirelessconnections in accordance with various aspects of the presentdisclosure;

FIG. 17 shows a flowchart illustrating a method for fast selection of anantenna subarray and beamforming for millimeter wave wirelessconnections in accordance with various aspects of the presentdisclosure;

FIG. 18 shows a flowchart illustrating a method for fast selection of anantenna subarray and beamforming for millimeter wave wirelessconnections in accordance with various aspects of the presentdisclosure;

FIG. 19 shows a flowchart illustrating a method for fast selection of anantenna subarray and beamforming for millimeter wave wirelessconnections in accordance with various aspects of the presentdisclosure;

FIG. 20 shows a flowchart illustrating a method for fast selection of anantenna subarray and beamforming for millimeter wave wirelessconnections in accordance with various aspects of the presentdisclosure; and

FIG. 21 illustrates an example of a process flow for fast selection ofan antenna subarray and beamforming for millimeter wave wirelessconnections in accordance with various aspects of the presentdisclosure;

DETAILED DESCRIPTION

The described features generally relate to improved systems, methods, orapparatuses for beam shaping at a millimeter wave base station and awireless device. As discussed above, millimeter wavelength signalsfrequently experience high path loss, and as a result, directional beamforming techniques may be used for uplink (UL) or downlink (DL)transmissions between a base station and a UE using millimeterwavelength frequencies. Directional beamforming techniques may enable atransmitter to transmit a signal onto a particular propagation path, andmay enable a receiver to receive a signal from a particular propagationpath.

The quality of link margins between the base station and the UE,however, may be dependent on a number of factors, including the locationof the UE in relation to the millimeter wave base station or the type ofcodebook utilized by the base station and the UE for beamforming. Forexample, while broader beam codebooks (e.g., coarse codebook orintermediate codebook) may occupy greater physical angular space bycompromising peak gains, the quality of signal experienced at the UE viabroader beams may be marginal compared to finer beams that may offergreater power gains. On the other hand, finer beam shapes, however, maysuffer from significant latency between the millimeter wave base stationand the UE because of the need to run through a large set of beams toensure coverage over the same physical angular coverage region.Therefore, optimally selecting a beam codebook from a plurality of beamcodebooks may reduce UE discovery latency and improve link margins.

The following description provides examples, and is not limiting of thescope, applicability, or examples set forth in the claims. Changes maybe made in the function and arrangement of elements discussed withoutdeparting from the scope of the disclosure. Various examples may omit,substitute, or add various procedures or components as appropriate. Forinstance, the methods described may be performed in an order differentfrom that described, and various steps may be added, omitted, orcombined. Also, features described with respect to some examples may becombined in other examples.

FIG. 1 illustrates an example of a wireless communications system 100 inaccordance with various aspects of the present disclosure. The system100 includes base stations 105, at least one UE 115, and a core network130. The core network 130 may provide user authentication, accessauthorization, tracking, internet protocol (IP) connectivity, and otheraccess, routing, or mobility functions. The base stations 105 interfacewith the core network 130 through backhaul links 132 (e.g., S1, etc.).The base stations 105 may perform radio configuration and scheduling forcommunication with the UEs 115, or may operate under the control of abase station controller (not shown). In various examples, the basestations 105 may communicate, either directly or indirectly (e.g.,through core network 130), with one another over backhaul links 134(e.g., X1, etc.), which may be wired or wireless communication links.

The base stations 105 may wirelessly communicate with the UEs 115 viaone or more base station antennas. Each of the base stations 105 mayprovide communication coverage for a respective geographic coverage area110. In some examples, base stations 105 may be referred to as a basetransceiver station, a radio base station, an access point, a radiotransceiver, a NodeB, eNodeB (eNB), Home NodeB, a Home eNodeB, or someother suitable terminology. The geographic coverage area 110 for a basestation 105 may be divided into sectors making up only a portion of thecoverage area (not shown). The wireless communications system 100 mayinclude base stations 105 of different types (e.g., macro or small cellbase stations). There may be overlapping geographic coverage areas 110for different technologies

In some examples, the wireless communications system 100 is a Long TermEvolution (LTE)/LTE-Advanced (LTE-A) network. In LTE/LTE-A networks, theterm evolved node B (eNB) may be generally used to describe the basestations 105, while the term UE may be generally used to describe theUEs 115. The wireless communications system 100 may be a heterogeneousLTE/LTE-A network in which different types of eNBs provide coverage forvarious geographical regions. For example, each eNB or base station 105may provide communication coverage for a macro cell, a small cell, orother types of cell. The term “cell” is a 3GPP term that can be used todescribe a base station, a carrier or component carrier associated witha base station, or a coverage area (e.g., sector, etc.) of a carrier orbase station, depending on context.

A macro cell generally covers a relatively large geographic area (e.g.,several kilometers in radius) and may allow unrestricted access by UEs115 with service subscriptions with the network provider. A small cellis a lower-powered base station, as compared with a macro cell, that mayoperate in the same or different (e.g., licensed, unlicensed, etc.)frequency bands as macro cells. Small cells may include pico cells,femto cells, and micro cells according to various examples. A pico cell,for example, may cover a small geographic area and may allowunrestricted access by UEs 115 with service subscriptions with thenetwork provider. A femto cell may also cover a small geographic area(e.g., a home) and may provide restricted access by UEs 115 having anassociation with the femto cell (e.g., UEs 115 in a closed subscribergroup (CSG), UEs 115 for users in the home, and the like). An eNB for amacro cell may be referred to as a macro eNB. An eNB for a small cellmay be referred to as a small cell eNB, a pico eNB, a femto eNB, or ahome eNB. An eNB may support one or multiple (e.g., two, three, four,and the like) cells (e.g., component carriers).

The wireless communications system 100 may support synchronous orasynchronous operation. For synchronous operation, the base stations 105may have similar frame timing, and transmissions from different basestations 105 may be approximately aligned in time. For asynchronousoperation, the base stations 105 may have different frame timing, andtransmissions from different base stations 105 may not be aligned intime. The techniques described herein may be used for either synchronousor asynchronous operations.

The communication networks that may accommodate some of the variousdisclosed examples may be packet-based networks that operate accordingto a layered protocol stack and data in the user plane may be based onthe IP. A radio link control (RLC) layer may perform packet segmentationand reassembly to communicate over logical channels. A medium accesscontrol (MAC) layer may perform priority handling and multiplexing oflogical channels into transport channels. The MAC layer may also usehybrid automatic repeat request (HARD) to provide retransmission at theMAC layer to improve link efficiency. In the control plane, the radioresource control (RRC) protocol layer may provide establishment,configuration, and maintenance of an RRC connection between a UE 115 andthe base stations 105. The RRC protocol layer may also be used for corenetwork 130 support of radio bearers for the user plane data. At thephysical (PHY) layer, the transport channels may be mapped to physicalchannels.

The UEs 115 may be dispersed throughout the wireless communicationssystem 100, and each UE 115 may be stationary or mobile. A UE 115 mayalso include or be referred to by those skilled in the art as a mobilestation, a subscriber station, a mobile unit, a subscriber unit, awireless unit, a remote unit, a mobile device, a wireless device, awireless communications device, a remote device, a mobile subscriberstation, an access terminal, a mobile terminal, a wireless terminal, aremote terminal, a handset, a user agent, a mobile client, a client, orsome other suitable terminology. A UE 115 may be a cellular phone, apersonal digital assistant (PDA), a wireless modem, a wirelesscommunication device, a handheld device, a tablet computer, a laptopcomputer, a cordless phone, a wireless local loop (WLL) station, or thelike. A UE may be able to communicate with various types of basestations and network equipment including macro eNBs, small cell eNBs,relay base stations, and the like.

The communication links 125 shown in wireless communications system 100may include uplink (UL) transmissions from a UE 115 to a base station105, or downlink (DL) transmissions, from a base station 105 to a UE115. The downlink transmissions may also be called forward linktransmissions while the uplink transmissions may also be called reverselink transmissions. Each communication link 125 may include one or morecarriers, where each carrier may be a signal made up of multiplesub-carriers (e.g., waveform signals of different frequencies) modulatedaccording to the various radio technologies described above. Eachmodulated signal may be sent on a different sub-carrier and may carrycontrol information (e.g., reference signals, control channels, etc.),overhead information, user data, etc. The communication links 125 maytransmit bidirectional communications using frequency division duplex(FDD) (e.g., using paired spectrum resources) or time division duplex(TDD) operation (e.g., using unpaired spectrum resources). Framestructures may be defined for FDD (e.g., frame structure type 1) and TDD(e.g., frame structure type 2).

In some embodiments of the system 100, base stations 105 or UEs 115 mayinclude multiple antennas for employing antenna diversity schemes toimprove communication quality and reliability between base stations 105and UEs 115. Additionally or alternately, base stations 105 or UEs 115may employ multiple input multiple output (MIMO) techniques that maytake advantage of multi-path environments to transmit multiple spatiallayers carrying the same or different coded data.

Wireless communications system 100 may support operation on multiplecells or carriers, a feature which may be referred to as carrieraggregation (CA) or multi-carrier operation. A carrier may also bereferred to as a component carrier (CC), a layer, a channel, etc. Theterms “carrier,” “component carrier,” “cell,” and “channel” may be usedinterchangeably herein. A UE 115 may be configured with multipledownlink CCs and one or more uplink CCs for carrier aggregation. Carrieraggregation may be used with both FDD and TDD component carriers.

A UE 115 attempting to access a wireless network may perform an initialcell search by detecting a primary synchronization signal (PSS) from abase station 105. The PSS may enable synchronization of slot timing andmay indicate a physical layer identity value. The UE 115 may thenreceive a secondary synchronization signal (SSS). The SSS may enableradio frame synchronization, and may provide a cell identity value,which may be combined with the physical layer identity value to identifythe cell. The SSS may also enable detection of a duplexing mode and acyclic prefix length. Some systems, such as TDD systems, may transmit anSSS but not a PSS. Both the PSS and the SSS may be located in thecentral 62 and 72 subcarriers of a carrier, respectively. Afterreceiving the PSS and SSS, the UE 115 may receive a master informationblock (MIB), which may be transmitted in the physical broadcast channel(PBCH). The MIB may contain system bandwidth information, a system framenumber (SFN), and a physical HARQ indicator channel (PHICH)configuration. After decoding the MIB, the UE 115 may receive one ormore system information block (SIBs). For example, SIB1 may contain cellaccess parameters and scheduling information for other SIBs. DecodingSIB1 may enable the UE 115 to receive SIB2. SIB2 may contain RRCconfiguration information related to random access channel (RACH)procedures, paging, physical uplink control channel (PUCCH), physicaluplink shared channel (PUSCH), power control, SRS, and cell barring.

After the UE 115 decodes SIB2, it may transmit a RACH preamble to a basestation 105. For example, the RACH preamble may be randomly selectedfrom a set of 64 predetermined sequences. This may enable the basestation 105 to distinguish between multiple UEs 115 trying to access thesystem simultaneously. The base station 105 may respond with a randomaccess response that provides an UL resource grant, a timing advance anda temporary cell radio network temporary identity (C-RNTI). The UE 115may then transmit an RRC connection request along with a temporarymobile subscriber identity (TMSI) (if the UE 115 has previously beenconnected to the same wireless network) or a random identifier. The RRCconnection request may also indicate the reason the UE 115 is connectingto the network (e.g., emergency, signaling, data exchange, etc.). Thebase station 105 may respond to the connection request with a contentionresolution message addressed to the UE 115, which may provide a newC-RNTI. If the UE 115 receives a contention resolution message with thecorrect identification, it may proceed with RRC setup. If the UE 115does not receive a contention resolution message (e.g., if there is aconflict with another UE 115), it may repeat the RACH process bytransmitting a new RACH preamble.

Wireless communications system 100 may operate in an ultra highfrequency (UHF) frequency region using frequency bands from 700 MHz to2600 MHz (2.6 GHz), although in some cases wireless local area network(WLAN) networks may use frequencies as high as 4 GHz. This region mayalso be known as the decimeter band, since the wavelengths range fromapproximately one decimeter to one meter in length. UHF waves maypropagate mainly by line of sight, and may be blocked by buildings andenvironmental features. However, the waves may penetrate wallssufficiently to provide service to UEs 115 located indoors. Transmissionof UHF waves is characterized by smaller antennas and shorter range(e.g., less than 100 km) compared to transmission using the smallerfrequencies (and longer waves) of the high frequency (HF) or very highfrequency (VHF) portion of the spectrum. In some cases, wirelesscommunications system 100 may also utilize extremely high frequency(EHF) portions of the spectrum (e.g., from 30 GHz to 300 GHz). Thisregion may also be known as the millimeter band, since the wavelengthsrange from approximately one millimeter to ten millimeters. Thus, EHFantennas may be even smaller and more closely spaced than UHF antennas.In some cases, this may facilitate use of antenna arrays within a UE 115(e.g., for directional beamforming). However, EHF transmissions may besubject to even greater atmospheric attenuation and shorter range thanUHF transmissions. In some examples, base stations 105 may be millimeterwave base stations configured to communicate with the UEs 115 utilizingdirectional beamforming. Additionally or alternately the base stations105 may be configured for hybrid communication utilizing bothlow-frequency carrier network (e.g., LTE) and a high frequency carriernetwork (e.g., millimeter wave).

In accordance with the present disclosure, a UE 115 may dynamicallyselect an optimal beam codebook in order to improve link margins withthe base stations 105. In some examples, a UE 115, during an initial UEdiscovery phase in millimeter access, may receive signals by physicalangle-based beam sweep initialized by the base station 105. The signalmay be transmitted by the base station 105 utilizing a default beamcodebook (e.g., coarse codebook) that utilizes broader beams with eachbeam covering a greater space (equivalently, a large 3-dB bandwidth) inthe physical angle space. The default beam codebook, however, may notoffer optimal power gains for beamforming, and thus negatively impactthe signal quality for UEs 115 that may not be in direct line of sight(LOS) of the base station. Therefore, the UE 115, upon receiving asignal from the millimeter wave base station 105, may estimate the SNRof the received signal and determine whether the received signalsatisfies signal quality thresholds established by the UE 115. In somecases, the SNR thresholds may be predetermined or dynamically adjustableby the UE 115.

In some examples, the UE 115, upon determining that the received signalis above a SNR threshold, may transmit a RACH signal with the beam sodetermining to convey the SNR information to the base station 105 andrequesting establishment of data communications. In some cases, the UE115 and the base station 105 may refine the beam to adjust for minorvariations in signal quality. Alternately if the UE 115 determines thatthe received signal is below a SNR threshold, the UE 115 may select analternate beam codebook (e.g., intermediate codebook or fine codebookwith a smaller 3-dB beamwidth for each beam) for directional beamformingthat may offer higher power gains. The selection of the alternate beamcodebook (i.e., intermediate codebook or fine codebook) may be signaledto the base station 105 over the UL channel. In some examples, theuplink transmission may direct the base station 105 to adjust the beamcodebooks at the base station 105 for subsequent transmissions.

Furthermore, millimeter wave signals may frequently experience high pathloss, and as a result, directional beam forming techniques may be usedfor uplink (UL) and/or downlink (DL) transmissions between a basestation and a UE using millimeter wave frequencies. Directionalbeamforming techniques may enable a transmitter to transmit a signalonto a particular propagation path, and may enable a receiver to receivea signal from a particular propagation path. In this case more than onesignal propagation path may exist between a UE and a base station.However, in some cases, the position of a user's hands (and parts of theuser's body) may interfere with signals received via directionalbeamforming. As a result, it may be ideal to scan through a plurality ofantenna subarrays at the UE 115-a in order to select the optimal antennasubarray, and further refine the beamforming vectors based on theselected antenna subarray.

FIG. 2 illustrates an example of a wireless communications subsystem 200in accordance with various aspects of the present disclosure. Wirelesscommunications subsystem 200 may include UE 115-a, which may be anexample of a UE 115 described above with reference to FIG. 1. Wirelesscommunications subsystem 200 may also include base station 105-a andbase station 105-b, which may be examples of base stations 105 describedabove with reference to FIG. 1. Base station 105-a and/or base station105-b may provide wireless communications service within coverage areas110-a and 110-b, respectively. Wireless communications subsystem 200illustrates an example where UE 115-a is located in the intersection ofcoverage areas 110-a and 110-b. However, in some cases UE 115-a may bewithin the coverage area of a single base station 105, or more than twobase stations 105.

UE 115-a, base station 105-a, and base station 105-b may each be capableof communicating using directional beamforming (e.g., using frequenciesin the millimeter band). Thus, in some cases UE 115-a may communicatewith base station 105-a using transmissions that follow more than onepath. For example, UE 115-a may communicate with base station 105-a viaa direct line-of-sight propagation path 205-a. UE 115-a and base station105-a may also communicate via an indirect propagation path 205-b, whichmay be reflected off a reflective surface 210-a (e.g., windows of abuilding). In some examples, a UE 115-a may initially establish a DLconnection and an UL connection via propagation path 205-a, and thenbase station 105-a may direct UE 115-a to use propagation path 205-b fortransmitting UL signals to base station 105-a (e.g., by providingdirectional beamforming configuration information associated withpropagation path 205-b). In another example, base station 105-a maydirect UE 115-a to establish an UL connection with (or handover to) basestation 105-b using propagation path 205-c. In some cases, a directline-of-sight propagation path may not be available and the UE 115-a andbase station 105-a may select from one or more indirect propagationpaths. In one example, the propagation path 205-c may be reflected off asecond reflective surface 210-b.

The propagation time for each path may be directly proportional to thedistance along the path. For example, the propagation time may beapproximately the length of the path divided by the speed of light.Thus, for example, a direct path such as propagation path 205-a may havea shorter propagation time than an indirect path to the same basestation 105 such as propagation path 205-b. In some examples of thepresent disclosure, the UE 115-a may dynamically select an optimal beamcodebook from a plurality of beam codebooks utilized at the UE 115-a andthe base station 105-a that offers best link margins for establishingcommunication. In some examples, the plurality of beam codebooks mayinclude any of a pseudo-omni beam pattern codebook, an antenna selectioncodebook, a coarse codebook of broad beams, an intermediate codebook ofslightly narrower beams, a fine codebook of narrowest beams, awireless-device specific codebook based on prior information at themillimeter wave base station about the wireless device, a beam negationcodebook such as a codebook of beams optimally designed to minimizeinterference due to simultaneous coordinated transmissions to multiplewireless devices, a codebook of beams trading off signal quality to aspecific wireless device at the cost of interference to other wirelessdevices, or, a combination of beamforming vectors from differentcodebooks.

FIG. 3 is a diagram of a system 300 for selecting an optimal antennasubarray and directional beamforming vector from a codebook ofbeamforming vectors. System 300 includes a base station 105-c and a UE115-b. In embodiments, base station 105-c may illustrate aspects of oneof the base stations or eNBs 105 while the UE 115-b may illustrateaspects of the mobile devices or UEs 115 as described above withreference to FIGS. 1-2.

The base station 105-c may have M transmit antennas 315. The UE 115-bmay have N receive antennas 335. System 300 may be used to employdiversity techniques such as transmit diversity, where multiple antennas(or antenna ports) transmit versions of a signal (e.g., delayed, coded,etc.) which maybe equalized at the receiver to provide diversity gain.The UE 115-b may also employ receive diversity, where signals frommultiple antennas are combined to provide diversity gain. System 300 mayemploy MIMO techniques to increase diversity gain, array gain (e.g.,beamforming, etc.), and/or spatial multiplexing gain.

In some examples of the present disclosure, the base station 105-c mayinclude larger number of antennas 335 than UE 115-b. For example,transmit M antennas for the base station may be 8×8 or 8×16 planararray, while the UE 115-b may typically include 4 or 6 antenna subarraysfor diversity reasons. Due to aperture considerations, each antennasubarray may typically include two (2) to eight (8) antennas. In someexamples each UE antenna subarray 335 may point at a subset of physicalangular regions. In some cases, a user holding the UE 115-b may block orinterfere with one or more antenna subarrays 335 based on the positionof the hand or other parts of the body. Hand blocking may adverselyimpact the signal quality of the receiver antennas 335.

In order to mitigate the impact of the hand/body blocking of antennas,the present disclosure provides a method for the UE 115-b to scanthrough a plurality of antenna subarrays 335 one at a time with a singlebeamforming vector transmitted by the base station 105-c to estimate thereceived SNR at a plurality of antenna subarrays 335. Based on theestimated SNR, the UE 115-b may select the best or ideal antennasubarray (e.g. antenna subarray 335-b) from a plurality of scannedantenna subarrays 335. For example, the UE 115-b may select an antennasubarray for which the received signal SNR is above a first SNRthreshold. In some examples, the SNR threshold may be predetermined oradapted based on user preference or some other protocol considerations.

In some examples, for further performance improvement or for reducingthe implementation complexity over the communication time frame, the UE115-b can receive an additional signal from the millimeter wave basestation, where the additional signal is beamformed on a plurality ofbeamforming vectors from a second codebook. The UE 115-b can then scan aplurality of beamforming vectors from the second codebook, and identifya second beamforming vector from the plurality of beamforming vectorsfrom the second codebook based on the scanning.

In an instance where the received SNR is below the first threshold, theUE 115-b may further determine whether the received SNR is above orbelow a second threshold. In some cases, the UE 115-b may suggest thebase station to scan through a coarse codebook of beamforming vectors aswell as modifying its own scan through a coarse codebook of beamformingvectors to select a best beam from either codebook that results in amoderate link margin. However, if the received SNR is below the secondthreshold level, the UE 115-b may offer a fallback position to suggestthe base station to scan through a finer codebook or a UE-specificcodebook to refine the beam on which the received signals are modulatedand also modify its own scan through a coarse/fine codebook ofbeamforming vectors to select the ideal beams based on the scan.Initiating the fallback procedures may result in slower discoveryperiods, but may offer improvement in the received signal quality.

Additionally or alternately, even in instances where the received signalis above the first threshold level, the UE 115-b may offer UE initiatedon-demand service to refine the beamforming vectors, and thereby achievehigher link margin for the subsequent data phase. For example, the UE115-b, upon determining that the initial received signal quality isabove the first threshold, may nonetheless request scan of the coarse,intermediate or fine beamforming codebook in order improve the linkmargins between the base station 105-c and the UE 115-b.

FIGS. 4A and 4B illustrate examples of situations in which the methodsof the present disclosure may be implemented. Wireless communicationssubsystems 402 and 404 for beam shaping may include UEs 115-c, which maybe an example of a UE 115 described above with reference to FIGS. 1-3.The wireless communications subsystems 402 and 404 may also include abase station 105-d, which may be an example of a base station 105described above with reference to FIGS. 1-3.

Referring first to the example 402 illustrated in FIG. 4A, the UE 115-cmay be in direct line of sight (LOS) of the base station 105-dcommunicating using default beam codebook (e.g., coarse codebook). Thedefault beam codebook 420 may offer greater coverage in space withreduced power gain levels. However, since the UE 115-c is in the line ofsight with the millimeter base station 105-d, utilization of the defaultbeam codebook 420 may not significantly negatively impact the SNR of thesignals received at the UE 115-c. As a result, the UE 115-c may also beconfigured to transmit and receive signals (i.e., control and datasignals) using UE default codebook 415. In some examples, the basestation 105-d may transmit a signal 405 during the UE discovery phase byusing baseline candidate beamforming vectors. The baseline candidatebeams may have a constant phase offset (CPO) across the number ofantenna elements. Upon receiving the signal 405, the UE 115-c maydetermine that the SNR of the received signal is above an establishedSNR threshold. As a result, the UE 115-c may transmit a RACH 410 withSNR and beam information to the base station 105-d and establish datalink communication between the base station 105-d and the UE 115-c. Insome examples, the UE 115-c and the base station 105-d may make minoradjustments to the beam shape to improve link margins.

However, turning now to example 404 illustrated in FIG. 4B, the UE 115-cmay be located outside the line of sight of the base station 105-d. Forexample, the UE 115-c may be located behind an obstacle 445 (e.g.,building), and thus signal 430 transmitted by the base station 105-d mayfirst be deflected off a reflector 440 (e.g., window of a building)prior to being received at the UE 115-c. As a result of the deflection,the quality of signal 430 received at the UE 115-c may be below anestablished SNR threshold. The signal quality may further be impacted bythe utilization of the default beam codebook 420 that offers reducedpower gains. Based on determining that the received signal 430 is belowan established SNR threshold, the UE 115-c may select an alternatecodebook 425 (e.g., intermediate or fine beam codebook) from a pluralityof available beam codebooks. In one example, the UE 115-c may switch theUE codebook to a fine beam codebook 425 that offers higher power gains,and transmit a RACH signal 435 to the base station 105-d.

In one or more examples, the UE 115-c may select the alternate beamcodebook based on incremental variations in the estimated SNR. Forexample, upon determining that the received signal 430 falls below afirst SNR threshold, the UE 115-c may further determine whether thereceived signal 430 is above or below a second SNR threshold. In theevent that the received signal 430 is below both the first SNR thresholdand the second SNR threshold, the UE 115-c may select a fine beamcodebook to improve link gains between the base station 105-d and the UE115-c. In contrast, if the UE 115-c determines that the received signal430 falls below a first SNR threshold, but is above a second SNRthreshold, the UE 115-c may select an intermediate beam codebook. Basedon the beam codebook selection, the UE 115-c may switch the UE 115-cbeam codebook and also transmit a RACH signal 435 to the base station105-d directing the base station 105-d to switch its base stationcodebook as well. In some examples, the RACH signal 435 may include SNRinformation and the selected beam information. In response to receivingthe RACH signal 435, the base station 105-d may switch its beamcodebooks to the beam codebook identified by the UE 115-d and transmitsubsequent signals utilizing the updated beam codebook.

FIG. 5 shows a block diagram of a wireless device 500 configured forbeam shaping at a millimeter wave base station and/or fast selection ofan antenna subarray at a wireless device in accordance with variousaspects of the present disclosure. Wireless device 500 may be an exampleof aspects of a UE 115 described with reference to FIGS. 1-4. Wirelessdevice 500 may include a receiver 505, a communication management module510, or a transmitter 515. Wireless device 500 may also include aprocessor. Each of these components may be in communication with eachother.

The components of wireless device 500 may, individually or collectively,be implemented with at least one application specific integrated circuit(ASIC) adapted to perform some or all of the applicable functions inhardware. Alternatively, the functions may be performed by one or moreother processing units (or cores), on at least one IC. In otherembodiments, other types of integrated circuits may be used (e.g.,Structured/Platform ASICs, a field programmable gate array (FPGA), oranother semi-custom IC), which may be programmed in any manner known inthe art. The functions of each unit may also be implemented, in whole orin part, with instructions embodied in a memory, formatted to beexecuted by one or more general or application-specific processors.

The receiver 505 may receive information such as packets, user data, orcontrol information associated with various information channels (e.g.,control channels, data channels, and information related to beam shapingand/or information related to antenna subarray selection at a millimeterwave base station and/or a wireless device, etc.). Information may bepassed on to the communications management module 510, and to othercomponents of wireless device 500.

The communications management module 510 may receive, at a wirelessdevice, a first signal from a millimeter wave base station using a firstbeam codebook, dynamically determine that a second beam codebook,different from the first beam codebook, is to be used on the transmittedfirst signal, and transmit a second signal to the millimeter wave basestation requesting the millimeter wave base station to use the secondbeam codebook. The communications management module 510 may also scan atleast a portion of a plurality of antenna subarrays with a plurality ofbeamforming vectors from a subarray selection codebook to identify aquality of the first signal received at the portion of the plurality ofantenna subarrays, and select an antenna subarray from the scannedportion of the plurality of antenna subarrays based at least in part onthe identified quality of the first signal.

The transmitter 515 may transmit signals received from other componentsof wireless device 500. In some embodiments, the transmitter 515 may becollocated with the receiver 505 in a transceiver module. Thetransmitter 515 may include a single antenna, or it may include aplurality of antennas.

FIG. 6 shows a block diagram of a wireless device 600 configured forbeam shaping at a millimeter wave base station and/or fast selection ofan antenna subarray at a wireless device in accordance with variousaspects of the present disclosure. Wireless device 600 may be an exampleof aspects of a wireless device 500 or a UE 115 described with referenceto FIGS. 1-5. Wireless device 600 may include a receiver 505-a, acommunication management module 510-a, or a transmitter 515-a. Wirelessdevice 600 may also include a processor. Each of these components may bein communication with each other. The communication management module510-a may also include a signal detection module 605, a beam adaptationmodule 610, and a codebook identification module 615.

The components of wireless device 600 may, individually or collectively,be implemented with at least one ASIC adapted to perform some or all ofthe applicable functions in hardware. Alternatively, the functions maybe performed by one or more other processing units (or cores), on atleast one IC. In other embodiments, other types of integrated circuitsmay be used (e.g., Structured/Platform ASICs, an FPGA, or anothersemi-custom IC), which may be programmed in any manner known in the art.The functions of each unit may also be implemented, in whole or in part,with instructions embodied in a memory, formatted to be executed by oneor more general or application-specific processors.

The receiver 505-a may receive information which may be passed on tocommunication management module 510-a, and to other components of UE.The communication management module 510-a may perform the operationsdescribed above with reference to FIG. 5. The transmitter 515-a maytransmit signals received from other components of wireless device 600.

The signal detection module 605 may receive, at a wireless device, afirst signal from a millimeter wave base station using a first beamcodebook as described above with reference to FIGS. 2-4. The signaldetection module 605 may also identify a first receiver beam codebookused at the wireless device as being associated with the first beamcodebook used by the millimeter wave base station. In some examples, thefirst signal may be a directional primary synchronization signal (DPSS).

The beam adaptation module 610 may dynamically determine that a secondbeam codebook, different from the first beam codebook, is to be used onthe transmitted first signal as described above with reference to FIGS.2-4. The beam adaptation module 610 may also switch from the firstreceiver beam codebook to a second receiver beam codebook associatedwith the second beam codebook used by the millimeter wave base station.In some examples, the second beam codebook may be selected in responseto determining that the quality of signal falls below the firstthreshold. In some examples, the first beam codebook may be a coarsecodebook and the second beam codebook may be selected from a groupcomprising at least one of a pseudo-omni beam pattern codebook, anantenna selection codebook, a coarse codebook of broad beams, anintermediate codebook of slightly narrower beams, a fine codebook ofnarrowest beams, a wireless-device specific codebook based on priorinformation at the millimeter wave base station about the wirelessdevice, a beam negation codebook such as a codebook of beams optimallydesigned to minimize interference due to simultaneous coordinatedtransmissions to multiple wireless devices, a codebook of beams tradingoff signal quality to a specific wireless device at the cost ofinterference to other wireless devices, or a combination of beamformingvectors from different codebooks.

The codebook identification module 615 may transmit a second signal tothe millimeter wave base station requesting the millimeter wave basestation to use the second beam codebook as described above withreference to FIGS. 2-4. The codebook identification module 615 may alsotransmit the second signal to the millimeter wave base stationidentifying the selected second beam codebook. In some examples, thesecond signal comprises a request for the millimeter wave base stationto switch to a second beam codebook. In some examples, the request canbe based at least in part on hardware and/or software complexity issuesfor the radio frequency chains (e.g. phase shifters, analog-to-digitalconverters, up/down converters and/or mixers, digital-to-analogconverters, radio frequency circuitry needed to establish the links, andthe like), maintenance of link issues, and/or performance improvementswith metrics such as rate, reliability, or a combination thereof. Thecodebook identification module 615 may also transmit the second signalvia a random access channel (RACH) using a coarse codebook. The codebookidentification module 615 may also transmit the second signal over alow-frequency carrier network coexisting with a millimeter wave carriernetwork. In some examples, the second signal comprises a distress signaltransmitted with a unique identification at a high code rate.

FIG. 7 shows a block diagram 700 of a communications management module510-b which may be a component of a wireless device 500 or a wirelessdevice 600 configured for beam shaping at a millimeter wave base stationand/or fast selection of an antenna subarray at a wireless device inaccordance with various aspects of the present disclosure. Thecommunications management module 510-b may be an example of aspects of acommunications management module 510 described with reference to FIGS.5-6. The communications management module 510-b may include a signaldetection module 605-a, a beam adaptation module 610-a, and a codebookidentification module 615-a. Each of these modules may perform thefunctions described above with reference to FIG. 6. The communicationsmanagement module 510-b may also include a signal-to-noise ratio (SNR)calculation module 705, and a beam codebook selection module 710.

The components of the communications management module 510-b may,individually or collectively, be implemented with at least one ASICadapted to perform some or all of the applicable functions in hardware.Alternatively, the functions may be performed by one or more otherprocessing units (or cores), on at least one IC. In other embodiments,other types of integrated circuits may be used (e.g.,Structured/Platform ASICs, an FPGA, or another semi-custom IC), whichmay be programmed in any manner known in the art. The functions of eachunit may also be implemented, in whole or in part, with instructionsembodied in a memory, formatted to be executed by one or more general orapplication-specific processors.

The SNR calculation module 705 may determine whether a quality of thereceived first signal is above or below a first threshold as describedabove with reference to FIGS. 2-4. The SNR calculation module 705 mayalso determine whether the quality of the first signal is above or belowa second threshold. The SNR calculation module 705 may also calculate asignal-to-noise ratio (SNR) of the first signal to determine a qualityof the first signal.

The beam codebook selection module 710 may dynamically select the secondbeam codebook based at least in part on the determining as describedabove with reference to FIGS. 2-4. The beam codebook selection module710 may also dynamically select the second beam codebook based at leastin part on the determining.

FIG. 8 shows a block diagram of a wireless device 800 configured forbeam shaping at a millimeter wave base station and/or fast selection ofan antenna subarray at a wireless device in accordance with variousaspects of the present disclosure. Wireless device 800 may be an exampleof aspects of a wireless device 500, a wireless device 600, or a UE 115described with reference to FIGS. 1-4, and 15. Wireless device 800 mayinclude a receiver 505-b, a communication management module 510-c, or atransmitter 515-b. Wireless device 800 may also include a processor.Each of these components may be in communication with each other. Thecommunication management module 510-c may also include a signaldetection module 805, an antenna scanning module 810, and an antennasubarray selection module 815.

The components of wireless device 800 may, individually or collectively,be implemented with at least one ASIC adapted to perform some or all ofthe applicable functions in hardware. Alternatively, the functions maybe performed by one or more other processing units (or cores), on atleast one IC. In other embodiments, other types of integrated circuitsmay be used (e.g., Structured/Platform ASICs, an FPGA, or anothersemi-custom IC), which may be programmed in any manner known in the art.The functions of each unit may also be implemented, in whole or in part,with instructions embodied in a memory, formatted to be executed by oneor more general or application-specific processors.

The receiver 505-b may receive information which may be passed on tocommunication management module 510-c, and to other components of UE115. The communication management module 510-c may perform theoperations described above with reference to FIG. 5. The transmitter515-b may transmit signals received from other components of wirelessdevice 800.

The signal detection module 805 may receive, at a wireless device, oneor more signals from a millimeter wave base station as described abovewith reference to FIGS. 2-4. In some examples, a received signal may bea directional primary synchronization signal (DPSS).

The antenna scanning module 810 may scan at least a portion of aplurality of antenna subarrays with a plurality of beamforming vectorsfrom a subarray selection codebook to identify a quality of the firstsignal received at the portion of the plurality of antenna subarrays asdescribed above with reference to FIGS. 2-4.

The antenna subarray selection module 815 may select an antenna subarrayfrom the scanned portion of the plurality of antenna subarrays based atleast in part on the identified quality of the first signal as describedabove with reference to FIGS. 2-4. The selection may include a coarsecodebook of broad beams covering a wide beamspace area optimallydesigned to minimize the wireless device discovery latency at the costof peak beamforming gain. The selection may also include an intermediatecodebook of slightly narrower beams covering a smaller beamspace areaand corresponding to another point in the tradeoff curve betweenwireless device discovery latency and peak beamforming gain. Theselection may also include a fine codebook of the narrowest beamscovering the smallest beamspace area and corresponding to the highestpeak beamforming gain. The selection may also include a codebookappropriately designed to mitigate near-field impairments at thewireless device. The selection may also include a codebook with aspecial structure appropriately designed to assist in channel estimationtasks at the wireless device. The selection may also include a codebookwith a special structure appropriately designed to assist inradio-frequency design, reduce system complexity or cost. The selectionmay also include any combination of beamforming vectors from differentcodebooks thereof.

FIG. 9 shows a block diagram 900 of a communications management module510-c which may be a component of a wireless device 500, a wirelessdevice 600, or a wireless device 800 configured for beam shaping at amillimeter wave base station and/or fast selection of an antennasubarray at a wireless device in accordance with various aspects of thepresent disclosure. The communications management module 510-c may be anexample of aspects of a communications management module 510 describedwith reference to FIGS. 5-8. The communications management module 510-cmay include a signal detection module 805-a, an antenna scanning module810-a, and an antenna subarray selection module 815-a. Each of thesemodules may perform the functions described above with reference to FIG.8. The communications management module 510-c may also include asignal-to-noise ratio (SNR) calculation module 905, a signaltransmission module 910, a beamforming vector scanning module 915, abeamforming identification module 920, and a threshold adaptation module925.

The components of the communications management module 510-c may,individually or collectively, be implemented with at least one ASICadapted to perform some or all of the applicable functions in hardware.Alternatively, the functions may be performed by one or more otherprocessing units (or cores), on at least one IC. In other embodiments,other types of integrated circuits may be used (e.g.,Structured/Platform ASICs, an FPGA, or another semi-custom IC), whichmay be programmed in any manner known in the art. The functions of eachunit may also be implemented, in whole or in part, with instructionsembodied in a memory, formatted to be executed by one or more general orapplication-specific processors.

The SNR calculation module 905 may determine whether the quality of thefirst signal at the selected antenna subarray is above or below a firstthreshold as described above with reference to FIGS. 2-4. The SNRcalculation module 905 may also determine that the quality of the firstsignal at the selected antenna subarray is below a second threshold. TheSNR calculation module 905 may also calculate a signal-to-noise ratio ofthe first signal to determine the quality of the first signal.

The signal transmission module 910 may transmit a second signal to themillimeter wave base station based at least in part on the determiningas described above with reference to FIGS. 2-4. The signal transmissionmodule 910 may also transmit the second signal via a RACH. The signaltransmission module 910 may also transmit the second signal over alow-frequency carrier network coexisting with a millimeter wave carriernetwork, and/or may transmit the second signal via a highly-codedlow-rate channel/network already established with a uniqueidentification number. In some examples, the second signal comprises asignal energy estimate, a beamforming vector index, information forbeamforming, or a combination thereof.

The beamforming vector scanning module 915 may scan a plurality ofbeamforming vectors from a coarse codebook upon determining that thequality of the first signal at the selected antenna subarray is belowthe first threshold as described above with reference to FIGS. 2-4.

The beamforming identification module 920 may identify a firstbeamforming vector from the plurality of beamforming vectors based atleast in part on the scanning as described above with reference to FIGS.2-4. The beamforming identification module 920 may also identify abeamforming vector from the plurality of beamforming vectors based atleast in part on the determining, wherein the beamforming vector isidentified from a fine codebook or a wireless device specific codebook.

The threshold adaptation module 925 may adapt the first threshold basedat least in part on a selection of a beamforming vector by the wirelessdevice as described above with reference to FIGS. 2-4.

FIG. 10 shows a diagram of a system 1000 including a UE 115-d configuredfor beam shaping at a millimeter wave base station and/or fast selectionof an antenna subarray at a wireless device in accordance with variousaspects of the present disclosure. System 1000 may include UE 115-d,which may be an example of a wireless device 500, a wireless device 600,a wireless device 800, or a UE 115 described above with reference toFIGS. 1-4. UE 115-d may include a communication management module 1010,which may be an example of a communication management module 510described with reference to FIGS. 5-9. UE 115-d may also include athreshold adjustment module 1025. UE 115-d may also include componentsfor bi-directional voice and data communications including componentsfor transmitting communications and components for receivingcommunications. For example, UE 115-d may communicate bi-directionallywith base station 105-e or UE 115-e.

The threshold adjustment module 1025 may adapt the first or second SNRthreshold levels as described above with reference to FIGS. 2-4. UE115-d may also include a processor module 1005, and memory 1015(including software (SW)) 1020, a transceiver module 1035, and one ormore antenna(s) 1040, each of which may communicate, directly orindirectly, with one another (e.g., via buses 1045). The transceivermodule 1035 may communicate bi-directionally, via the antenna(s) 1040 orwired or wireless links, with one or more networks, as described above.For example, the transceiver module 1035 may communicatebi-directionally with a base station 105 or another UE 115. Thetransceiver module 1035 may include a modem to modulate the packets andprovide the modulated packets to the antenna(s) 1040 for transmission,and to demodulate packets received from the antenna(s) 1040. While UE115-d may include a single antenna 1040, UE 115-d may also have multipleantennas 1040 capable of concurrently transmitting or receiving multiplewireless transmissions.

The on-demand scanning module 1030 may initiate an on-demand search toidentify a second beamforming vector from a plurality of beamformingvectors at the millimeter wave base station, wherein the secondbeamforming vector is identified from a group comprising a pseudo-omnibeam pattern codebook, an antenna selection codebook, a coarse codebook,an intermediate codebook, a fine codebook, a near-field impairmentmitigation codebook, a channel estimation codebook, a complexityreduction codebook, or a wireless device specific codebook, as describedabove with reference to FIGS. 2-4.

The memory 1015 may include random access memory (RAM) and read onlymemory (ROM). The memory 1015 may store computer-readable,computer-executable software/firmware code 1020 including instructionsthat, when executed, cause the processor module 1005 to perform variousfunctions described herein (e.g., Techniques for beam shaping at amillimeter wave base station and a wireless device, etc.). Alternately,the software/firmware code 1020 may not be directly executable by theprocessor module 1005 but cause a computer (e.g., when compiled andexecuted) to perform functions described herein. The processor module1005 may include an intelligent hardware device, (e.g., a centralprocessing unit (CPU), a microcontroller, an ASIC, etc.)

FIG. 11 shows a flowchart illustrating a method 1100 for beam shaping ata millimeter wave base station and a wireless device in accordance withvarious aspects of the present disclosure. The operations of method 1100may be implemented by a UE 115 or its components as described withreference to FIGS. 1-10. For example, the operations of method 1100 maybe performed by a communication management modules 510 or 1010 asdescribed with reference to FIGS. 5-10. In some examples, a UE 115 mayexecute a set of codes to control the functional elements of the UE 115to perform the functions described below. Additionally or alternately,the UE 115 may perform aspects the functions described below usingspecial-purpose hardware.

At block 1105, the UE 115 may receive, at a wireless device, a firstsignal from a millimeter wave base station using a first beam codebookas described above with reference to FIGS. 2-4. In certain examples, theoperations of block 1105 may be performed by the signal detection module605 as described above with reference to FIGS. 6 and 7.

At block 1110, the UE 115 may dynamically determine that a second beamcodebook, different from the first beam codebook, is to be used on thetransmitted first signal as described above with reference to FIGS. 2-4.In certain examples, the operations of block 1110 may be performed bythe beam adaptation module 610 as described above with reference toFIGS. 6 and 7.

At block 1115, the UE 115 may transmit a second signal to the millimeterwave base station requesting the millimeter wave base station to use thesecond beam codebook as described above with reference to FIGS. 2-4. Incertain examples, the operations of block 1115 may be performed by thecodebook identification module 615 as described above with reference toFIGS. 6 and 7.

FIG. 12 shows a flowchart illustrating a method 1200 for beam shaping ata millimeter wave base station and a wireless device in accordance withvarious aspects of the present disclosure. The operations of method 1200may be implemented by a UE 115 or its components as described withreference to FIGS. 1-10. For example, the operations of method 1200 maybe performed by a communications management module 510 or 1010 asdescribed with reference to FIGS. 5-10. In some examples, a UE 115 mayexecute a set of codes to control the functional elements of the UE 115to perform the functions described below. Additionally or alternately,the UE 115 may perform aspects the functions described below usingspecial-purpose hardware. The method 1200 may also incorporate aspectsof method 1100 of FIG. 11.

At block 1205, the UE 115 may receive, at a wireless device, a firstsignal from a millimeter wave base station using a first beam codebookas described above with reference to FIGS. 2-4. In certain examples, theoperations of block 1205 may be performed by the signal detection module605 as described above with reference to FIGS. 6 and 7.

At block 1210, the UE 115 may determine whether a quality of thereceived first signal is above or below a first threshold as describedabove with reference to FIGS. 2-4. In certain examples, the operationsof block 1110 may be performed by the SNR calculation module 705 asdescribed above with reference to FIG. 7.

At block 1215, the UE 115 may dynamically select the second beamcodebook, different from the first beam codebook based at least in parton the determining as described above with reference to FIGS. 2-4. Incertain examples, the operations of block 1215 may be performed by thebeam codebook selection module 710 as described above with reference toFIG. 8.

At block 1220, the UE 115 may transmit a second signal to the millimeterwave base station requesting the millimeter wave base station to use thesecond beam codebook as described above with reference to FIGS. 2-4. Incertain examples, the operations of block 1220 may be performed by thecodebook identification module 615 as described above with reference toFIGS. 6 and 7.

FIG. 13 shows a flowchart illustrating a method 1300 for beam shaping ata millimeter wave base station and a wireless device in accordance withvarious aspects of the present disclosure. The operations of method 1300may be implemented by a UE 115 or its components as described withreference to FIGS. 1-10. For example, the operations of method 1300 maybe performed by a communications management module 510 or 1010 asdescribed with reference to FIGS. 5-10. In some examples, a UE 115 mayexecute a set of codes to control the functional elements of the UE 115to perform the functions described below. Additionally or alternately,the UE 115 may perform aspects the functions described below usingspecial-purpose hardware. The method 1300 may also incorporate aspectsof methods 1100, and 1200 of FIGS. 11-12.

At block 1305, the UE 115 may receive, at a wireless device, a firstsignal from a millimeter wave base station using a first beam codebookas described above with reference to FIGS. 2-4. In certain examples, theoperations of block 1305 may be performed by the signal detection module605 as described above with reference to FIGS. 6 and 7.

At block 1310, the UE 115 may determine whether the quality of the firstsignal is above or below a second threshold as described above withreference to FIGS. 2-4. In certain examples, the operations of block1310 may be performed by the SNR calculation module 705 as describedabove with reference to FIG. 7.

At block 1315, the UE 115, upon determining that the first signal isbelow a first threshold, may determine whether the quality of the firstsignal is above or below a second threshold as described above withreference to FIGS. 2-4. In certain examples, the operations of block1315 may be performed by the SNR calculation module 705 as describedabove with reference to FIG. 7.

At block 1320, the UE 115 may dynamically select the second beamcodebook based at least in part on the determining as described abovewith reference to FIGS. 2-4. In certain examples, the operations ofblock 1320 may be performed by the beam codebook selection module 710 asdescribed above with reference to FIG. 7.

At block 1325, the UE 115 may transmit a second signal to the millimeterwave base station requesting the millimeter wave base station to use thesecond beam codebook as described above with reference to FIGS. 2-4. Incertain examples, the operations of block 1315 may be performed by thecodebook identification module 615 as described above with reference toFIGS. 6 and 7.

FIG. 14 shows a flowchart illustrating a method 1400 for beam shaping ata millimeter wave base station and a wireless device in accordance withvarious aspects of the present disclosure. The operations of method 1400may be implemented by a UE 115 or its components as described withreference to FIGS. 1-10. For example, the operations of method 1400 maybe performed by a communication management module 510 or 1010 asdescribed with reference to FIGS. 5-10. In some examples, a UE 115 mayexecute a set of codes to control the functional elements of the UE 115to perform the functions described below. Additionally or alternately,the UE 115 may perform aspects the functions described below usingspecial-purpose hardware. The method 1400 may also incorporate aspectsof methods 1100, 1200, and 1300 of FIGS. 11-13.

At block 1405, the UE 115 may receive, at a wireless device, a firstsignal from a millimeter wave base station using a first beam codebookas described above with reference to FIGS. 2-4. In certain examples, theoperations of block 1405 may be performed by the signal detection module605 as described above with reference to FIGS. 6 and 7.

At block 1410, the UE 115 may dynamically determine that a second beamcodebook, different from the first beam codebook, is to be used on thereceived first signal as described above with reference to FIGS. 2-4. Incertain examples, the operations of block 1410 may be performed by thebeam adaptation module 610 as described above with reference to FIGS. 6and 7.

At block 1415, the UE 115 may transmit a second signal to the millimeterwave base station requesting the millimeter wave base station to use thesecond beam codebook as described above with reference to FIGS. 2-4. Incertain examples, the operations of block 1415 may be performed by thecodebook identification module 615 as described above with reference toFIGS. 6 and 7.

At block 1420, the UE 115 may identify a first receiver beam codebookused at the wireless device as being associated with the first beamcodebook used by the millimeter wave base station as described abovewith reference to FIGS. 2-4. In certain examples, the operations ofblock 1420 may be performed by the signal detection module 605 asdescribed above with reference to FIGS. 6 and 7.

At block 1425, the UE 115 may switch from the first receiver beamcodebook to a second receiver beam codebook associated with the secondbeam codebook used by the millimeter wave base station as describedabove with reference to FIGS. 2-4. In certain examples, the operationsof block 1425 may be performed by the beam adaptation module 610 asdescribed above with reference to FIGS. 6 and 7.

Thus, methods 1100, 1200, 1300, and 1400 may provide for beam shaping ata millimeter wave base station and a wireless device. It should be notedthat methods 1100, 1200, 1300, and 1400 describe possibleimplementation, and that the operations and the steps may be rearrangedor otherwise modified such that other implementations are possible. Insome examples, aspects from two or more of the methods 1100, 1200, 1300,and 1400 may be combined.

FIG. 15 illustrates an example of a process flow 1500 for beam shapingat a millimeter wave base station and a wireless device in accordancewith various aspects of the present disclosure. Process flow 1500 may beexecuted by a UE 115 or base station 105, which may be an example of aUE 115 or base station 105 described above with reference to FIGS. 1-4.

At block 1505, millimeter wave base station and the UE may selectdefault beam codebooks to transmit and receive signals. In someexamples, the base station and the UE may start with coarsest codebookon either side. At block 1510, the base station and the UE may select aplurality of SNR threshold levels (i.e., first SNR threshold and secondSNR threshold). In some examples, the SNR threshold levels may bepredetermined or dynamically adjusted based on user preference or otherprotocol considerations driven by the user. For example, the SNRthreshold levels may be selected based on the type and amount of data tobe transmitted.

Upon selecting the default beam codebook and SNR threshold levels, theUE 115 and the base station 105 may enter UE discovery phase. At block1515, the UE may receive directional primary synchronization signal(DPSS) waveform from the base station along a plurality of beamformingvectors from the default beam codebook. The UE may combine the receivedwaveforms across a subarray of antennas at the UE from the UE selecteddefault beam codebook. At block 1520, the UE may estimate the SNR of thereceived signal and determine whether the SNR of the received signal isabove a first SNR threshold. If the UE determines that the SNR of thereceived signal is above the first SNR threshold, the UE, at block 1525may transmit signal energy estimates, corresponding base stationbeamforming vector index and other relevant information for beamformingto the base station via RACH. Subsequently, at block 1530, the UE andthe base station may enter post-RACH phase. At block 1535, the UE andthe base station may refine the beam based on the received beam and SNRinformation. At block 1540, the UE and the base station may enter dataphase and establish data communication with the selected beams.

Alternately, if the UE, at block 1520, determines that the SNR of thereceived signal is below the first threshold, the UE may furtherdetermine whether the received signal also falls below a second SNRthreshold at block 1545. If the signal quality of the received signalfalls below the second SNR threshold, the UE, at block 1550, may selecta low-frequency back-up link option from the UE to base station (ifavailable) or issue a distress signal. In some examples, the distresssignal may request the base station to switch its beam codebook to afine codebook. The UE may also switch its codebook to a fine codebookbased on the issued distress signal. However, if the received signal isabove a second SNR threshold, the UE, at block 1555, may issue signal tothe base station requesting the base station switch its codebook tointermediate codebook, while maintaining coarse codebook for the UE.Upon selecting appropriate codebooks, the process flow 1500 may repeatat block 1505 utilizing the updated codebook selections (i.e., blocks1550 and 1555). In some examples, the SNR threshold levels at block 1510may also be adapted based on the codebook selections.

FIG. 16 shows a flowchart illustrating a method 1600 for fast selectionof an antenna subarray and beamforming for millimeter wave wirelessconnections in accordance with various aspects of the presentdisclosure. The operations of method 1600 may be implemented by a UE 115or its components as described with reference to FIGS. 1-4. For example,the operations of method 1600 may be performed by a communicationsmanagement module 510 or 1010 as described with reference to FIGS. 5-10.In some examples, a UE 115 may execute a set of codes to control thefunctional elements of the UE 115 to perform the functions describedbelow. Additionally or alternately, the UE 115 may perform aspects thefunctions described below using special-purpose hardware.

At block 1605, the UE 115 may receive, at a wireless device, a firstsignal from a millimeter wave base station, the first signal beamformedon a plurality of beamforming vectors from a first codebook, asdescribed above with reference to FIGS. 2-4. In certain examples, theoperations of block 1605 may be performed by the signal detection module805 as described above with reference to FIGS. 8-9.

At block 1610, the UE 115 may scan at least a portion of a plurality ofantenna subarrays to identify a quality of the first signal received atthe portion of the plurality of antenna subarrays as described abovewith reference to FIGS. 2-4. In one embodiment, the portion of theplurality of antennas may be scanned with a plurality of beamformingvectors from a subarray selection codebook. In certain examples, theoperations of block 1610 may be performed by the antenna scanning module810 as described above with reference to FIGS. 8-9.

At block 1615, the UE 115 may select an antenna subarray from thescanned portion of the plurality of antenna subarrays based at least inpart on the identified quality of the first signal as described abovewith reference to FIGS. 2-4. In certain examples, the operations ofblock 1615 may be performed by the antenna subarray selection module 815as described above with reference to FIGS. 8-9.

FIG. 17 shows a flowchart illustrating a method 1700 for fast selectionof an antenna subarray and beamforming for millimeter wave wirelessconnections in accordance with various aspects of the presentdisclosure. The operations of method 1700 may be implemented by a UE 115or its components as described with reference to FIGS. 1-4. For example,the operations of method 1700 may be performed by a communicationsmanagement module 510 or 1010 as described with reference to FIGS. 5-10.In some examples, a UE 115 may execute a set of codes to control thefunctional elements of the UE 115 to perform the functions describedbelow. Additionally or alternately, the UE 115 may perform aspects thefunctions described below using special-purpose hardware. The method1700 may also incorporate aspects of method 1600 of FIG. 16.

At block 1705, the UE 115 may receive, at a wireless device, a firstsignal from a millimeter wave base station, the first signal beamformedon a plurality of beamforming vectors from a first codebook, asdescribed above with reference to FIGS. 2-4. In certain examples, theoperations of block 1705 may be performed by the signal detection module805 as described above with reference to FIGS. 8 and 9.

At block 1710, the UE 115 may scan at least a portion of a plurality ofantenna subarrays with a plurality of beamforming vectors from asubarray selection codebook to identify a quality of the first signalreceived at the portion of the plurality of antenna subarrays asdescribed above with reference to FIGS. 2-4. In certain examples, theoperations of block 1710 may be performed by the antenna scanning module810 as described above with reference to FIGS. 8 and 9.

At block 1715, the UE 115 may select an antenna subarray from thescanned portion of the plurality of antenna subarrays based at least inpart on the identified quality of the first signal as described abovewith reference to FIGS. 2-4. In certain examples, the operations ofblock 1715 may be performed by the antenna subarray selection module 815as described above with reference to FIGS. 8 and 9.

At block 1720, the UE 115 may determine whether the quality of the firstsignal at the selected antenna subarray is above or below a firstthreshold as described above with reference to FIGS. 2-4. In certainexamples, the operations of block 1720 may be performed by the SNRcalculation module 905 as described above with reference to FIG. 9.

At block 1725, the UE 115 may transmit a second signal to the millimeterwave base station based at least in part on the determining as describedabove with reference to FIGS. 2-4. In certain examples, the operationsof block 1725 may be performed by the signal transmission module 910 asdescribed above with reference to FIG. 9.

FIG. 18 shows a flowchart illustrating a method 1800 for fast selectionof an antenna subarray and beamforming for millimeter wave wirelessconnections in accordance with various aspects of the presentdisclosure. The operations of method 1800 may be implemented by a UE 115or its components as described with reference to FIGS. 1-4. For example,the operations of method 1800 may be performed by a communicationsmanagement module 510 or 1010 as described with reference to FIGS. 5-10.In some examples, a UE 115 may execute a set of codes to control thefunctional elements of the UE 115 to perform the functions describedbelow. Additionally or alternately, the UE 115 may perform aspects thefunctions described below using special-purpose hardware. The method1800 may also incorporate aspects of methods 1600 or 1700 of FIGS.16-17.

At block 1805, the UE 115 may receive, at a wireless device, a firstsignal from a millimeter wave base station, the first signal beamformedon a plurality of beamforming vectors from a first codebook, asdescribed above with reference to FIGS. 2-4. In certain examples, theoperations of block 1805 may be performed by the signal detection module805 as described above with reference to FIGS. 8 and 9.

At block 1810, the UE 115 may scan at least a portion of a plurality ofantenna subarrays with a plurality of beamforming vectors from asubarray selection codebook to identify a quality of the first signalreceived at the portion of the plurality of antenna subarrays asdescribed above with reference to FIGS. 2-4. In certain examples, theoperations of block 1710 may be performed by the antenna scanning module810 as described above with reference to FIGS. 8 and 9.

At block 1815, the UE 115 may select an antenna subarray from thescanned portion of the plurality of antenna subarrays based at least inpart on the identified quality of the first signal as described abovewith reference to FIGS. 2-4. In certain examples, the operations ofblock 1815 may be performed by the antenna subarray selection module 815as described above with reference to FIGS. 8 and 9.

At block 1820, the UE 115 may determine whether the quality of the firstsignal at the selected antenna subarray is above or below a firstthreshold as described above with reference to FIGS. 2-4. In certainexamples, the operations of block 1720 may be performed by the SNRcalculation module 905 as described above with reference to FIG. 9.

At block 1825, the UE 115 may transmit a second signal to the millimeterwave base station based at least in part on the determining as describedabove with reference to FIGS. 2-4. In certain examples, the operationsof block 1725 may be performed by the signal transmission module 910 asdescribed above with reference to FIG. 9.

At block 1830, the UE 115 may receive a third signal from the millimeterwave base station, the third signal beamformed on a plurality ofbeamforming vectors from a second codebook as described above withreference to FIGS. 2-4. In certain examples, the operations of block1815 may be performed by the signal detection module 805 as describedabove with reference to FIGS. 8 and 9.

At block 1835, the UE 115 may scan a plurality of beamforming vectorsfrom the second codebook as described above with reference to FIGS. 2-4.In certain examples, the operations of block 1835 may be performed bythe antenna scanning module 810 as described above with reference toFIGS. 8 and 9.

At block 1840, the UE 115 may identify a second beamforming vector fromthe plurality of beamforming vectors from the second codebook based onthe scanning of the second codebook as described above with reference toFIGS. 2-4. In certain examples, the operations of block 1815 may beperformed by the antenna subarray selection module 815 as describedabove with reference to FIGS. 8 and 9.

FIG. 19 shows a flowchart illustrating a method 1900 for fast selectionof an antenna subarray and beamforming for millimeter wave wirelessconnections in accordance with various aspects of the presentdisclosure. The operations of method 1800 may be implemented by a UE 115or its components as described with reference to FIGS. 1-4. For example,the operations of method 1900 may be performed by a communicationsmanagement module 510 or 1010 as described with reference to FIGS. 5-10.In some examples, a UE 115 may execute a set of codes to control thefunctional elements of the UE 115 to perform the functions describedbelow. Additionally or alternately, the UE 115 may perform aspects thefunctions described below using special-purpose hardware. The method1800 may also incorporate aspects of methods 1600, 1700, and 1800 ofFIGS. 16-18.

At block 1905, the UE 115 may receive, at a wireless device, a firstsignal from a millimeter wave base station, the first signal beamformedon a plurality of beamforming vectors from a first codebook, asdescribed above with reference to FIGS. 2-4. In certain examples, theoperations of block 1905 may be performed by the signal detection module805 as described above with reference to FIGS. 8 and 9.

At block 1910, the UE 115 may scan at least a portion of a plurality ofantenna subarrays with a plurality of beamforming vectors from asubarray selection codebook to identify the quality of the first signalreceived at the portion of the plurality of antenna subarrays asdescribed above with reference to FIGS. 2-4. In certain examples, theoperations of block 1910 may be performed by the antenna scanning module810 as described above with reference to FIGS. 8 and 9.

At block 1915, the UE 115 may select an antenna subarray from thescanned portion of the plurality of antenna subarrays based at least inpart on the identified quality of the first signal as described abovewith reference to FIGS. 2-4. In certain examples, the operations ofblock 1915 may be performed by the antenna subarray selection module 815as described above with reference to FIGS. 8 and 9.

At block 1920, the UE 115 may determine whether the quality of the firstsignal at the selected antenna subarray is above or below a firstthreshold as described above with reference to FIGS. 2-4. In certainexamples, the operations of block 1920 may be performed by the SNRcalculation module 905 as described above with reference to FIG. 9.

At block 1925, the UE 115 may transmit a second signal to the millimeterwave base station based at least in part on the determining as describedabove with reference to FIGS. 2-4. In certain examples, the operationsof block 1925 may be performed by the signal transmission module 910 asdescribed above with reference to FIG. 9.

At block 1930, the UE 115 may scan a plurality of beamforming vectorsfrom a coarse codebook upon determining that the quality of the firstsignal at the selected antenna subarray is below the first threshold asdescribed above with reference to FIGS. 2-4. In certain examples, theoperations of block 1930 may be performed by the beamforming vectorscanning module 915 as described above with reference to FIG. 9.

At block 1935, the UE 115 may identify a first beamforming vector fromthe plurality of beamforming vectors based at least in part on thescanning as described above with reference to FIGS. 2-4. In certainexamples, the operations of block 1935 may be performed by thebeamforming identification module 920 as described above with referenceto FIG. 9.

FIG. 20 shows a flowchart illustrating a method 1900 for fast selectionof an antenna subarray and beamforming for millimeter wave wirelessconnections in accordance with various aspects of the presentdisclosure. The operations of method 2000 may be implemented by a UE 115or its components as described with reference to FIGS. 1-4. For example,the operations of method 2000 may be performed by a communicationsmanagement module 510 or 1010 as described with reference to FIGS. 5-10.In some examples, a UE 115 may execute a set of codes to control thefunctional elements of the UE 115 to perform the functions describedbelow. Additionally or alternately, the UE 115 may perform aspects thefunctions described below using special-purpose hardware. The method1900 may also incorporate aspects of methods 1600, 1700, 1800, and 1900of FIGS. 16-19.

At block 2005, the UE 115 may receive, at a wireless device, a firstsignal from a millimeter wave base station, the first signal beamformedon a plurality of beamforming vectors from a first codebook, asdescribed above with reference to FIGS. 2-4. In certain examples, theoperations of block 2005 may be performed by the signal detection module805 as described above with reference to FIGS. 8 and 9.

At block 2010, the UE 115 may scan at least a portion of a plurality ofantenna subarrays with a plurality of beamforming vectors from asubarray selection codebook to identify a quality of the first signalreceived at the portion of the plurality of antenna subarrays asdescribed above with reference to FIGS. 2-4. In certain examples, theoperations of block 2010 may be performed by the antenna scanning module810 as described above with reference to FIGS. 8 and 9.

At block 2015, the UE 115 may select an antenna subarray from thescanned portion of the plurality of antenna subarrays based at least inpart on the identified quality of the first signal as described abovewith reference to FIGS. 2-4. In certain examples, the operations ofblock 2015 may be performed by the antenna subarray selection module 815as described above with reference to FIGS. 8-9.

At block 2020, the UE 115 may scan a plurality of beamforming vectorsfrom a coarse codebook upon determining that the quality of the firstsignal at the selected antenna subarray is below the first threshold asdescribed above with reference to FIGS. 2-4. In certain examples, theoperations of block 2020 may be performed by the beamforming vectorscanning module 915 as described above with reference to FIG. 9.

At block 2025, the UE 115 may identify a first beamforming vector fromthe plurality of beamforming vectors based at least in part on thescanning as described above with reference to FIGS. 2-4. In certainexamples, the operations of block 2025 may be performed by thebeamforming identification module 920 as described above with referenceto FIG. 9.

At block 2030, the UE 115 may determine that the quality of the firstsignal at the selected antenna subarray is below a second threshold asdescribed above with reference to FIGS. 2-4. In certain examples, theoperations of block 2030 may be performed by the SNR calculation module905 as described above with reference to FIG. 9.

At block 2035, the UE 115 may identify a second beamforming vector fromthe plurality of beamforming vectors based at least in part on thedetermining, wherein the second beamforming vector is identified from afine codebook or a wireless device specific codebook as described abovewith reference to FIGS. 2-4. In certain examples, the operations ofblock 2035 may be performed by the beamforming identification module 920as described above with reference to FIG. 9.

Thus, methods 1600, 1700, 1800, 1900, and 2000 may provide for fastselection of an antenna subarray and beamforming for millimeter wavewireless connections. It should be noted that methods 1600, 1700, 1800,1900, and 2000 describe possible implementation, and that the operationsand the steps may be rearranged or otherwise modified such that otherimplementations are possible. In some examples, aspects from two or moreof the methods 1600, 1700, 1800, 1900, and 2000 may be combined.

FIG. 21 illustrates an example of a process flow 2100 for fast selectionof an antenna subarray and beamforming for millimeter wave wirelessconnections in accordance with various aspects of the presentdisclosure. Process flow 2100 may be executed by UE 115, which may be anexample of a UE 115 described above with reference to FIGS. 2-4.

At block 2105, the UE 115 may receive a first signal from a millimeterwave base station during the UE discovery phase. In some examples, theUE may scan through a plurality of antenna subarrays one at a time witha single beamforming vector to estimate the received SNR at eachsubarray.

At block 2110, the UE 115 may select an antenna subarray from thescanned portion of the set of antenna subarrays based on the identifiedquality of the first signal. In some examples, the antenna subarray maybe selected to maximize the UE's estimate of signal energy forsubsequent UE signal processing.

At block 2115, the UE 115 may determine whether the quality of the firstsignal at the selected antenna subarray may be satisfactory for the dataphase. In the event that the UE 115 determines that the UE's estimate ofsignal energy for best base station beamforming vector from the selectedantenna subarray exceeds an appropriately chosen SNR threshold, the UE115, at block 2120 may convey signal energy estimates, millimeter wavebase station beamforming vector index and other relevant information forbeamforming to the millimeter base station via the RACH. Subsequentlythe UE 115 and the base station may initiate data phase ofcommunication.

However, if the UE 115, at block 2115 determines that the UE's estimateof signal energy for best base station beamforming vector from theselected antenna subarray falls below the chosen SNR threshold, the UE115 may select a coarse codebook of beamforming vectors at both the basestation end and the UE end at the selected antenna subarray.Additionally or alternately, the UE and the base station may adapt SNRthresholds based on the selected coarse codebook. After the selection ofa coarse codebook sweep at the selected antenna subarray, the basestation may transmit a directional primary synchronization signal (DPSS)waveform along each of the beamforming vectors from the selectedcodebook.

In response, at block 2125, the UE may determine whether the SNR forreceived signals utilizing the updated codebook is above anotherappropriately chosen threshold level. In the event that the receivedsignals exceed the threshold level, the UE, at block 2130, may conveysignal energy estimates, millimeter wave base station beamforming vectorindex and other relevant information for beamforming to the millimeterbase station via the RACH. However, if the SNR for received signalsfalls below the threshold level, the UE 115, at block 2135 may select afiner codebook switch at the selected antenna subarray and at the basestation. At block 2140, the UE may again determine whether the updatedcodebook selection improves the SNR for the received signals. If thereceived signal is above the second SNR threshold, the UE may enter thedata phase at block 2130. However, if at block 2145, the UE 115determines that the SNR is below the second threshold, the UE 115 mayagain scan a plurality of antenna subarrays for an improved link margin.Additionally or alternately, the UE 115 at block 2150 may also determinewhether an alternate path exists between the base station and the UE 115that may offer improved signal quality. In the event that a better pathexists between the base station and the UE, the UE 115 may initiate theprocess flow 2100 again with a plurality of antenna subarrays for thealternate path. In contrast, if no alternate path exists, the UE 115, atblock 2155 may disconnect process flow 2100 for a predetermined timeperiod.

The detailed description set forth above in connection with the appendeddrawings describes exemplary embodiments and does not represent all theembodiments that may be implemented or that are within the scope of theclaims. The term “exemplary” used throughout this description means“serving as an example, instance, or illustration,” and not “preferred”or “advantageous over other embodiments.” The detailed descriptionincludes specific details for the purpose of providing an understandingof the described techniques. These techniques, however, may be practicedwithout these specific details. In some instances, well-known structuresand devices are shown in block diagram form in order to avoid obscuringthe concepts of the described embodiments.

Information and signals may be represented using any of a variety ofdifferent technologies and techniques. For example, data, instructions,commands, information, signals, bits, symbols, and chips that may bereferenced throughout the above description may be represented byvoltages, currents, electromagnetic waves, magnetic fields or particles,optical fields or particles, or any combination thereof.

The various illustrative blocks and modules described in connection withthe disclosure herein may be implemented or performed with ageneral-purpose processor, a digital signal processor (DSP), an ASIC, anFPGA or other programmable logic device, discrete gate or transistorlogic, discrete hardware components, or any combination thereof designedto perform the functions described herein. A general-purpose processormay be a microprocessor, but in the alternative, the processor may beany conventional processor, controller, microcontroller, or statemachine. A processor may also be implemented as a combination ofcomputing devices (e.g., a combination of a DSP and a microprocessor,multiple microprocessors, one or more microprocessors in conjunctionwith a DSP core, or any other such configuration).

The functions described herein may be implemented in hardware, softwareexecuted by a processor, firmware, or any combination thereof. Ifimplemented in software executed by a processor, the functions may bestored on or transmitted over as one or more instructions or code on acomputer-readable medium. Other examples and implementations are withinthe scope of the disclosure and appended claims. For example, due to thenature of software, functions described above can be implemented usingsoftware executed by a processor, hardware, firmware, hardwiring, orcombinations of any of these. Features implementing functions may alsobe physically located at various positions, including being distributedsuch that portions of functions are implemented at different physicallocations. Also, as used herein, including in the claims, “or” as usedin a list of items (for example, a list of items prefaced by a phrasesuch as “at least one of” or “one or more of”) indicates an inclusivelist such that, for example, a list of [at least one of A, B, or C]means A or B or C or AB or AC or BC or ABC (i.e., A and B and C).

Computer-readable media includes both non-transitory computer storagemedia and communication media including any medium that facilitatestransfer of a computer program from one place to another. Anon-transitory storage medium may be any available medium that can beaccessed by a general purpose or special purpose computer. By way ofexample, and not limitation, non-transitory computer-readable media cancomprise RAM, ROM, electrically erasable programmable read only memory(EEPROM), compact disk (CD) ROM or other optical disk storage, magneticdisk storage or other magnetic storage devices, or any othernon-transitory medium that can be used to carry or store desired programcode means in the form of instructions or data structures and that canbe accessed by a general-purpose or special-purpose computer, or ageneral-purpose or special-purpose processor. Also, any connection isproperly termed a computer-readable medium. For example, if the softwareis transmitted from a website, server, or other remote source using acoaxial cable, fiber optic cable, twisted pair, digital subscriber line(DSL), or wireless technologies such as infrared, radio, and microwave,then the coaxial cable, fiber optic cable, twisted pair, DSL, orwireless technologies such as infrared, radio, and microwave areincluded in the definition of medium. Disk and disc, as used herein,include CD, laser disc, optical disc, digital versatile disc (DVD),floppy disk and Blu-ray disc where disks usually reproduce datamagnetically, while discs reproduce data optically with lasers.Combinations of the above are also included within the scope ofcomputer-readable media.

The previous description of the disclosure is provided to enable aperson skilled in the art to make or use the disclosure. Variousmodifications to the disclosure will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other variations without departing from the scope of thedisclosure. Thus, the disclosure is not to be limited to the examplesand designs described herein but is to be accorded the broadest scopeconsistent with the principles and novel features disclosed herein.

Techniques described herein may be used for various wirelesscommunications systems such as code division multiple access (CDMA),time division multiple access (TDMA), frequency division multiplexing(FDM)A, orthogonal frequency division multiple access (OFDMA), singlecarrier frequency division multiple access (SC-FDMA), and other systems.The terms “system” and “network” are often used interchangeably. A CDMAsystem may implement a radio technology such as CDMA2000, UniversalTerrestrial Radio Access (UTRA), etc. CDMA2000 covers IS-2000, IS-95,and IS-856 standards. IS-2000 Releases 0 and A are commonly referred toas CDMA2000 1×, 1×, etc. IS-856 (TIA-856) is commonly referred to asCDMA2000 1×EV-DO, High Rate Packet Data (HRPD), etc. UTRA includesWideband CDMA (WCDMA) and other variants of CDMA. A TDMA system mayimplement a radio technology such as Global System for MobileCommunications (GSM). An OFDMA system may implement a radio technologysuch as Ultra Mobile Broadband (UMB), Evolved UTRA (E-UTRA), IEEE 802.11(Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDM, etc. UTRA andE-UTRA are part of Universal Mobile Telecommunications system (UMTS).3GPP Long Term Evolution (LTE) and LTE-Advanced (LTE-A) are new releasesof Universal Mobile Telecommunications System (UMTS) that use E-UTRA.UTRA, E-UTRA, UMTS, LTE, LTE-A, and Global System for Mobilecommunications (GSM) are described in documents from an organizationnamed “3rd Generation Partnership Project” (3GPP). CDMA2000 and UMB aredescribed in documents from an organization named “3rd GenerationPartnership Project 2” (3GPP2). The techniques described herein may beused for the systems and radio technologies mentioned above as well asother systems and radio technologies. The description above, however,describes an LTE system for purposes of example, and LTE terminology isused in much of the description above, although the techniques areapplicable beyond LTE applications.

What is claimed is:
 1. A method of communications at a wireless device,the method comprising: receiving, at the wireless device, a first signalfrom a millimeter wave base station, the first signal beamformed on aplurality of beamforming vectors from a first codebook; scanning aplurality of antenna subarrays, each of the plurality of antennasubarrays comprising a different subset of a plurality of antennas ofthe wireless device, to identify a quality of the first signal asreceived by each of the plurality of antenna subarrays; and selectingone of the plurality of antenna subarrays based at least in part on theidentified quality of the first signal as received by at least one ofthe plurality of antenna subarrays.
 2. The method of claim 1, whereinthe scanning further comprises: scanning the plurality of antennasubarrays with a plurality of beamforming vectors from a subarrayselection codebook to identify the quality of the first signal asreceived by each of the plurality of antenna subarrays.
 3. The method ofclaim 2, further comprising: selecting a first beamforming vector fromthe plurality of beamforming vectors from the subarray selectioncodebook for a respective subarray from the plurality of antennasubarrays based at least on the identified quality of the first signal.4. The method of claim 2, wherein the subarray selection codebookcomprises at least one of: a pseudo-omni beam pattern codebook; anantenna selection codebook; a coarse codebook; an intermediate codebook;a fine codebook; a codebook designed to mitigate near-field impairments;a codebook designed to assist in channel estimation; or a codebookdesigned to assist in radio-frequency design, reduce system complexity,or reduce system cost; or a combination of beamforming vectors fromdifferent codebooks.
 5. The method of claim 1, further comprising:initiating an on-demand search to identify a second beamforming vectorfrom a plurality of beamforming vectors at the millimeter wave basestation, wherein the second beamforming vector is identified from agroup comprising at least one of a coarse codebook, an intermediatecodebook, a fine codebook, a near-field impairment mitigation codebook,a channel estimation codebook, a complexity reduction codebook, or awireless device specific codebook.
 6. The method of claim 1, furthercomprising: determining whether the quality of the first signal at theselected antenna subarray is above or below a first threshold; andtransmitting a second signal to the millimeter wave base station basedat least in part on the determining.
 7. The method of claim 6, furthercomprising: receiving, at the wireless device, a third signal from themillimeter wave base station, the third signal beamformed on a pluralityof beamforming vectors from a second codebook; scanning a plurality ofbeamforming vectors from the second codebook; and identifying a secondbeamforming vector from a plurality of beamforming vectors from thesecond codebook based at least in part on the scanning a plurality ofbeamforming vectors from the second codebook.
 8. The method of claim 6,further comprising: adapting the first threshold based at least in parton a selection of a beamforming vector by the wireless device.
 9. Themethod of claim 6, further comprising: transmitting the second signalvia a random access channel (RACH).
 10. The method of claim 6, furthercomprising: determining that a signal quality of the first signal at theselected subarray is below the first threshold; and transmitting thesecond signal over a low-frequency carrier network coexisting with amillimeter wave carrier network based at least in part on determiningthat the signal quality of the first signal at the selected subarray isbelow the first threshold.
 11. The method of claim 6, furthercomprising: transmitting the second signal via a highly-coded low-ratecommunication link already established with a unique identification. 12.The method of claim 6, wherein the second signal comprises a signalenergy estimate, a beamforming vector index, information forbeamforming, or a combination thereof.
 13. The method of claim 6,further comprising: calculating a signal-to-noise ratio of the firstsignal to determine the quality of the first signal.
 14. The method ofclaim 1, wherein the first signal is a directional primarysynchronization signal.
 15. An apparatus for wireless communications,comprising: a processor; memory in electronic communication with theprocessor; and instructions stored in the memory; wherein theinstructions are executable by the processor to: receive, at a wirelessdevice, a first signal from a millimeter wave base station, the firstsignal beamformed on a plurality of beamforming vectors from a firstcodebook; scan a plurality of antenna subarrays, each of the pluralityof antenna subarrays comprising a different subset of a plurality ofantennas of the wireless device, to identify a quality of the firstsignal as received by each of the plurality of antenna subarrays; andselect one of the plurality of antenna subarrays based at least in parton the identified quality of the first signal as received by at leastone of the plurality of antenna subarrays.
 16. The apparatus of claim15, wherein the instructions are executable by the processor to: scanthe plurality of antenna subarrays with a plurality of beamformingvectors from a subarray selection codebook to identify the quality ofthe first signal as received by each of the plurality of antennasubarrays.
 17. The apparatus of claim 16, wherein the instructions areexecutable by the processor to: select a first beamforming vector fromthe plurality of beamforming vectors from the subarray selectioncodebook for that subarray from the scanned portion of the plurality ofantenna subarrays based at least on the identified quality of the firstsignal.
 18. The apparatus of claim 16, wherein the subarray selectioncodebook comprises at least one of: a pseudo-omni beam pattern codebook;an antenna selection codebook; a coarse codebook; an intermediatecodebook; a fine codebook; a codebook designed to mitigate near-fieldimpairments; a codebook designed to assist in channel estimation; acodebook designed to assist in radio-frequency design, reduce systemcomplexity, or reduce system cost; or a combination of beamformingvectors from different codebooks.
 19. The apparatus of claim 15, whereinthe instructions are executable by the processor to: initiate anon-demand search to identify a second beamforming vector from aplurality of beamforming vectors at the millimeter wave base station,wherein the second beamforming vector is identified from a groupcomprising at least one of a coarse codebook, an intermediate codebook,a fine codebook, a near-field impairment mitigation codebook, a channelestimation codebook, a complexity reduction codebook, or a wirelessdevice specific codebook.
 20. The apparatus of claim 15, wherein theinstructions are executable by the processor to: determine whether thequality of the first signal at the selected antenna subarray is above orbelow a first threshold; and transmit a second signal to the millimeterwave base station based at least in part on the determining.
 21. Theapparatus of claim 20, wherein the instructions are executable by theprocessor to: receive, at the wireless device, a third signal from themillimeter wave base station, the third signal beamformed on a pluralityof beamforming vectors from a second codebook; scan a plurality ofbeamforming vectors from the second codebook; and identify a secondbeamforming vector from a plurality of beamforming vectors from thesecond codebook based at least in part on the scanning a plurality ofbeamforming vectors from the second codebook.
 22. The apparatus of claim20, wherein the instructions are executable by the processor to: adaptthe first threshold based at least in part on a selection of abeamforming vector by the wireless device.
 23. The apparatus of claim20, wherein the instructions are executable by the processor to:transmit the second signal via a random access channel (RACH).
 24. Theapparatus of claim 20, wherein the instructions are executable by theprocessor to: determine that a signal quality of the first signal at theselected subarray is below the first threshold; and transmit the secondsignal over a low-frequency carrier network coexisting with a millimeterwave carrier network based at least in part on determining that thesignal quality of the first signal at the selected subarray is below thefirst threshold.
 25. The apparatus of claim 20, wherein the instructionsare executable by the processor to: transmit the second signal via ahighly-coded low-rate communication link already established with aunique identification.
 26. The apparatus of claim 20, wherein the secondsignal comprises a signal energy estimate, a beamforming vector index,information for beamforming, or a combination thereof.
 27. The apparatusof claim 20, wherein the instructions are executable by the processorto: calculate a signal-to-noise ratio of the first signal to determinethe quality of the first signal.
 28. The apparatus of claim 15, whereinthe first signal is a directional primary synchronization signal.
 29. Anapparatus for wireless communications, comprising: means for receiving,at a wireless device, a first signal from a millimeter wave basestation, the first signal beamformed on a plurality of beamformingvectors from a first codebook; means for scanning a plurality of antennasubarrays, each of the plurality of antenna subarrays comprising adifferent subset of a plurality of antennas of the wireless device, toidentify a quality of the first signal as received by each of theplurality of antenna subarrays; and means for selecting one of theplurality of antenna subarrays based at least in part on the identifiedquality of the first signal as received by at least one of the pluralityof antenna subarrays.
 30. The apparatus of claim 29, further comprising:means for scanning the plurality of antenna subarrays with a pluralityof beamforming vectors from a subarray selection codebook to identifythe quality of the first signal as received by each of the plurality ofantenna subarrays.
 31. The apparatus of claim 30, further comprising:means for selecting a first beamforming vector from the plurality ofbeamforming vectors from the subarray selection codebook for arespective subarray from the plurality of antenna subarrays based atleast on the identified quality of the first signal.
 32. The apparatusof claim 30, wherein the subarray selection codebook comprises at leastone of: a pseudo-omni beam pattern codebook; an antenna selectioncodebook; a coarse codebook; an intermediate codebook; a fine codebook;a codebook designed to mitigate near-field impairments; a codebookdesigned to assist in channel estimation; a codebook designed to assistin radio-frequency design, reduce system complexity, or reduce systemcost; or or a combination of beamforming vectors from differentcodebooks.
 33. The apparatus of claim 29, further comprising: means forinitiating an on-demand search to identify a second beamforming vectorfrom a plurality of beamforming vectors at the millimeter wave basestation, wherein the second beamforming vector is identified from agroup comprising at least one of a coarse codebook, an intermediatecodebook, a fine codebook, a near-field impairment mitigation codebook,a channel estimation codebook, a complexity reduction codebook, or awireless device specific codebook.
 34. The apparatus of claim 29,further comprising means for determining whether the quality of thefirst signal at the selected antenna subarray is above or below a firstthreshold; and means for transmitting a second signal to the millimeterwave base station based at least in part on the determining.
 35. Theapparatus of claim 18, further comprising: means for adapting the firstthreshold based at least in part on a selection of a beamforming vectorby the wireless device.
 36. The apparatus of claim 18, furthercomprising: means for transmitting the second signal via a random accesschannel (RACH).
 37. The apparatus of claim 18, further comprising: meansfor determining that a signal quality of the first signal at theselected subarray is below the first threshold; and means fortransmitting the second signal over a low-frequency carrier networkcoexisting with a millimeter wave carrier network based at least in parton determining that the signal quality of the first signal at theselected subarray is below the first threshold.
 38. The apparatus ofclaim 18, further comprising: means for transmitting the second signalvia a highly-coded low-rate communication link already established witha unique identification.
 39. The apparatus of claim 18, wherein thesecond signal comprises a signal energy estimate, a beamforming vectorindex, information for beamforming, or a combination thereof.
 40. Theapparatus of claim 34, further comprising: means for calculating asignal-to-noise ratio of the first signal to determine the quality ofthe first signal.
 41. The apparatus of claim 34, further comprising:means for receiving, at the wireless device, a third signal from themillimeter wave base station, the third signal beamformed on a pluralityof beamforming vectors from a second codebook; means for scanning aplurality of beamforming vectors from the second codebook; means foridentifying a second beamforming vector from a plurality of beamformingvectors from the second codebook based at least in part on the scanninga plurality of beamforming vectors from the second codebook.
 42. Theapparatus of claim 29, wherein the first signal is a directional primarysynchronization signal.
 43. A non-transitory computer-readable mediumstoring code for communication at a wireless device, the code comprisinginstructions executable to: receive, at the wireless device, a firstsignal from a millimeter wave base station, the first signal beamformedon a plurality of beamforming vectors from a first codebook; scan aplurality of antenna subarrays, each of the plurality of antennasubarrays comprising a different subset of a plurality of antennas ofthe wireless device, to identify a quality of the first signal asreceived by each of the plurality of antenna subarrays; and select oneof the plurality of antenna subarrays based at least in part on theidentified quality of the first signal as received by at least one ofthe plurality of antenna subarrays.
 44. The non-transitorycomputer-readable medium of claim 43, wherein the scanning furthercomprises: scanning the plurality of antenna subarrays with a pluralityof beamforming vectors from a subarray selection codebook to identifythe quality of the first signal as received by each of the plurality ofantenna subarrays.
 45. The non-transitory computer-readable medium ofclaim 44, further comprising: selecting a first beamforming vector fromthe plurality of beamforming vectors from the subarray selectioncodebook for a respective subarray from the plurality of antennasubarrays based at least on the identified quality of the first signal.46. The non-transitory computer-readable medium of claim 44, wherein thesubarray selection codebook comprises at least one of: a pseudo-omnibeam pattern codebook; an antenna selection codebook; a coarse codebook;an intermediate codebook; a fine codebook; a codebook designed tomitigate near-field impairments; a codebook designed to assist inchannel estimation; or a codebook designed to assist in radio-frequencydesign, reduce system complexity, or reduce system cost; or acombination of beamforming vectors from different codebooks.
 47. Thenon-transitory computer-readable medium of claim 43, further comprising:initiating an on-demand search to identify a second beamforming vectorfrom a plurality of beamforming vectors at the millimeter wave basestation, wherein the second beamforming vector is identified from agroup comprising at least one of a coarse codebook, an intermediatecodebook, a fine codebook, a near-field impairment mitigation codebook,a channel estimation codebook, a complexity reduction codebook, or awireless device specific codebook.
 48. The non-transitorycomputer-readable medium of claim 43, further comprising: determiningwhether the quality of the first signal at the selected antenna subarrayis above or below a first threshold; and transmitting a second signal tothe millimeter wave base station based at least in part on thedetermining.
 49. The non-transitory computer-readable medium of claim48, further comprising: receiving, at the wireless device, a thirdsignal from the millimeter wave base station, the third signalbeamformed on a plurality of beamforming vectors from a second codebook;scanning a plurality of beamforming vectors from the second codebook;and identifying a second beamforming vector from a plurality ofbeamforming vectors from the second codebook based at least in part onthe scanning a plurality of beamforming vectors from the secondcodebook.
 50. The non-transitory computer-readable medium of claim 48,further comprising: adapting the first threshold based at least in parton a selection of a beamforming vector by the wireless device.
 51. Thenon-transitory computer-readable medium of claim 48, further comprising:transmitting the second signal via a random access channel (RACH). 52.The non-transitory computer-readable medium of claim 48, furthercomprising: determining that a signal quality of the first signal at theselected subarray is below the first threshold; and transmitting thesecond signal over a low-frequency carrier network coexisting with amillimeter wave carrier network based at least in part on determiningthat the signal quality of the first signal at the selected subarray isbelow the first threshold.
 53. The non-transitory computer-readablemedium of claim 48, further comprising: transmitting the second signalvia a highly-coded low-rate communication link already established witha unique identification.
 54. The non-transitory computer-readable mediumof claim 48, wherein the second signal comprises a signal energyestimate, a beamforming vector index, information for beamforming, or acombination thereof.
 55. The non-transitory computer-readable medium ofclaim 48, further comprising: calculating a signal-to-noise ratio of thefirst signal to determine the quality of the first signal.
 56. Thenon-transitory computer-readable medium of claim 43, wherein the firstsignal is a directional primary synchronization signal.